Insects

145 - 66 mya Cretaceous

Animals Springtails Mites Woodlice Worms

With the advance of flowering plants - the angiosperms, there was a relatively fast development of an existing world – soil - to accommodate the faster evolution of insects and other arthropods running about making the most of the broadleaf fall, which helped flowers to colonise the world

Earwigs

Earwigs, like those we see today, first appeared in the early part of this period (Engel et al 2002). There were earlier sorts in earlier periods, that have become extinct. As hemimetabolous insects, they have 5 moults before becoming adults.

Close links

Recent molecular evidence supports this. “Unexpectedly, after adding the new sequences into the phylogenetic analyses, all dipluran hexamerins (storage proteins) including CspHex1 grouped together and as sister to the insect hexamerins, with high likelihood and Bayesian support. Our analysis supports a single origin of the hexamerins in Hexapoda, and suggests the close relationship between Diplura and Insecta" (Xie & Luan 2014)

Dipluran ancestors?

This would fit with the earlier hypothesis that hemimetabolous insects, like earwigs, may have evolved in soils from ancestors like Diplurans. Could Japygid diplurans have evolved into earwigs? Earwigs appear around a hundred million years after diplurans. Their key characteristic cerci of Japygids are said to lead to occasional ‘confusion’ with earwigs. The Diplurans, which we know were around over 300 mya, may have given rise to some more hemimetabolic insects, fitting in with Ghilarov’s theory that many insects evolved ‘through’ soils. Newly emerging insects would include earwigs. Those that we know then today, emerged in this period. “Neodermapterans (new earwigs) first appear in the Early Cretaceous but might have originated in the Late Jurassic. Certainly, definitive neodermapterans …are known by the Middle Cretaceous" (Zhao et al 2010). They have a series of moults and are mostly nocturnal and often hide in small, moist crevices during the day. Leaf litter would be ideal as it provided a safer environment for soil dwelling diplurans to evolve into earwigs – with their final moult having wings. Their wings are pretty stubby and they rarely fly preferring to stay among the litter.

Look at the nymphal stages of earwig development above, and see how close the early stages resemble diplurans. Diplurans are one of three main groups along with springtails and proturan that we’ve met before that have internal mouthparts. Diplurans are not earwigs, but I can't help but think they could have evolved into them, especially as earwigs inhabit the soil surface, and thus still in soil-like environment but have the potential to fly. Their mouthparts - the distinguishing feature, would have evolved from those (endognatha - diplurans ) that needed protection from soil to those that are external (ectognatha as in insects), would make sense.

Is it too much to imagine that the diplurans ran around for millions of years, but some had extra moults. They have unusual powers to regenerate lost body parts, so they may have acquired a harder cuticle capable of living on top of the litter layer, rather than in it. They may have developed rudimentary wings, which help them fly into the air. They had over a hundred million years of trials. Earwigs are active at night and hide during the day in cracks and crevices, which suggests to me they could have evolved out of the soil. Rather than seeking links through shapes or genes, when look at the environment where evolution may occur, it may help determine the evolutionary relations - phylogeny.

Phylogeny

Phylogentic analyses supports monophlyly(one ancestor) of Hexapoda and suggests paraphlyly(many ancestors) of Endognatha(those with internal mouthparts)" (Sasaki et al 2013) They looked for insights into the origin of hexapods and the processes involved in the adaptation of insects to life on land. They quote "A Carboniferous dipluran fossil showed that only Diplura of Entognatha (mainly insects) shares an ancestral ground plan with Ectognatha, suggesting a close relationship between Diplura and Ectognatha. Comparative embryological evidence and phylogenetic analyses based on morphological and some molecular data (EF-1α, EF-2, and RNA polymerase II sequences) also suggest that a relationship exists between Diplura and Ectognatha." It is not a big step to go from 'Entognatha - where mouthparts are protected - which would be necessary moving through soil, to external mouthparts of Ectognatha, physically feasible above ground.

Ants

We saw the first appearances of ants in the previous period. Now they are being found in amber, “For example, an early ant Haidomyrmex , from mid-Cretaceous Myanmar amber displays exceptionally specialized mouthparts of the Maxillolabiate mouthpart (see below) class.”

A recent study found ants, now found in terrestrial ecosystems the world over, appeared first about 150 mya but diversified only about 100 million years ago in concert - with the flowering plants. "These resilient insects, now found in terrestrial ecosystems the world over, apparently began to diversify only about 100 million years ago in concert with the flowering plants.“

During the Cretaceous period, a few species of primitive ants ranged widely on Northern super continent Laurasia. They were scarce in comparison to other insects, representing about 1% of the insect population.

Ants are one of those insects which use the soil to build their nests. While they alter the physical structure of soil, for their workers to forage far for food - which can be just about anything, like the milk of aphids, insects and small living or dead invertebrates, as well as the sap of plants and various fruits. Later they evolve to eat fungi, but that is 50 million years away.

Cretaceous worker ant
Most Cretaceous ants belong to stem-group Formicidae

Ants carrying soil mites

Ants & Oribatids

The increased numbers and distribution of oribatids provided a new food source for the the ants which appeared in the previous period. They had ant nests over the soil, with their scavenging workers scouting the surroundings for building matter, then food. There would be loads of mites which, as we’ve seen, had been running round for millions of years, as lower Oribatid. They can roll up in a tight ball to withstand dry conditions. This would have also put them in good stead against predators. But ants seem to have learned the trick, and it may be this which naturally selected oribatids with stronger cuticles - higher oribatids in this period (See how Staphylinid beetles eat oribatids)

Pheidole ant

We came across E O Wilson earlier, saying that oribatid mites were the most important animal group in terms of the world’s biodiversity. He also wrote a famous paper, using ‘cafeteria experiments’ with forest soil and litter. He “obtained evidence that species of Pheidole (ant found all over the world) prey on a wide array of slow-moving invertebrates, favouring those of approximately their own size. The most frequent prey were oribatid mites, a disproportion evidently due in part to the abundance of these organisms. The ants have no difficulty breaking through the calcified exoskeleton of the mites. For millions of years oribatids would have made difficult eating, and their environment of deep and dark pretty protective. Once nearer the surface, and with the new invaders, they were now vulnerable – and in their millions." ‘My all-time favourite scientific paper’ in Small Pond Science.

2 years after the Wilson paper, Ralph Saporito sorted out that mite alkaloids end up in ants, which are eaten by poison frogs and used for their chemical defences. (Saporito et al 2007). The frogs can also eat the mites too.

Other sorts of ants – like fungus growing and leaf-cutting species, evolved a long time after this.

Bees

Many bees also form nests, often solitary, in soil. Bees probably played an important part in the coevolution of flowering plants. It seems that bees lost the wasp waist as they consumed the pollen, which they fed, along with nectar, to their larvae.

“The earliest bee, Melittosphex, from Myanmar amber, (right) bears the typical head and mouthpart features of distinctive tridentate mandibles and branched hairs of Glossate mouthparts in modern bees associated with pollination”

Insect Pollination

We think it is just bees which can pollinate flowers, but wasps, butterflies, moths all feed off nectar to give the energy for sex, and accidentally pollinate. Some better than others. Bees are specific, flies more generalist. Apparently they need nectar, as sex takes energy. The flowers provide that. Other insects also accidentally pollinate - like ants and termites.

Butterflies

Butterflies arose in the middle of this Cretaceous. "Butterflies originated from nocturnal, herbivorous moth ancestors around 101.4 million years ago (Ma) (102.5–100.0 Ma), providing evidence for a mid-Cretaceous origin of butterflies..butterflies dispersed out of the Neotropics at a much higher rate than that of any other dispersal route " (Kawahara et al 2023)

"Of the 39 current butterfly subfamilies, eight survived the mass extinction of the late Cretaceous—the same event that wiped out the dinosaurs. Many butterflies pass their pupal stage in soil, where they are protected against wintry conditions so can re-emerge the following year and as adults become important flower pollinators.

Some evidence reveals that these animals fluttered about 200 mya – even before flowering plants came along.

The colourful butterflies we know only emerged after the dinosuars.

Termites

We often think termites and ants are related as they both are eusocial and have large nests built into and out of soil. Although these insects are often called "white ants" they are not ants, and not even closely related.

The termites’ family tree indicate that they evolved from cockroaches, being a sister group to wood eating cockroaches, Cryptocercus. The first fossil records are about 150-125mya - the Early Cretaceous, but established dominance in tropical soils about 50mya. due to their guts (Bucek et al 2019).

Dung Beetles

Dinosaurs dominated and left ever more dung - some would have been over a ton a lump. Luckily we have people who are really interested in that. You may have seen how dung beetles roll the lumps of dung, so It is hard to imagine a dung beetle rolling a 15cm diameter dinosaur dung with its back legs. But there would have been a lot of dinosaur dung, fully fermented plant matter mixed with methane.

Using ancient fossils and DNA from 450 modern scarab beetle species, dung-eating beetles are estimated to have popped up (or is that pooped up?) at least 115 million years ago - 30 million years earlier than previously thought. At the time, the only mammals around were tiny and would have produced dry dung pellets—poor eating for a dung beetle . But the beetles' origin does line up with the age of the dinosaurs and the rise of flowering plants. The first larva of dung beetles evolved in dinosaur poo. One for the pub quiz.

Modern-day dung beetles mostly eat the excrement of mammals, like cows and elephants. They lay their eggs in dung, so their larvae have a good food source, and help break it donw further so soil creatures can nibble the breakdown products even further. They can live in dry conditions and provide great starting point for aerobic digestion.

Once flowering plants evolved, those were eaten and pooped out by dinosaurs, and then offered the beetles more nutrition and less difficult fibre to work through, which was an enticing enough package to get some beetles to really specialise in collecting and eating poo.

Paleoscatologists at work

‘Paleoscatologists’ have, quite possibly, the best job description ever: “fossil dung scientists". They like examining 'coprolites' - fossil dung. They are 'trace' fossils, ie not the actual body.

Co-extinction?

It has been long debated whether the key event in the evolution of dung beetles (Scarabaeidae: Scarabaeinae) was an adaptation to feeding on dinosaur or mammalian dung. Here we present molecular evidence to show that the origin of dung beetles occurred in the middle of the Cretaceous, likely in association with dinosaur dung, but more surprisingly the timing is consistent with the rise of the angiosperms. We hypothesize that the switch in dinosaur diet to incorporate more nutritious and less fibrous angiosperm foliage provided a palatable dung source that ultimately created a new niche for diversification.

Given the well-accepted mass extinction of non-avian dinosaurs at the Cretaceous-Paleogene boundary, we examine a potential co-extinction of dung beetles due to the loss of an important evolutionary resource, i.e., dinosaur dung. The biogeography of dung beetles is also examined to explore the previously proposed “out of Africa” hypothesis. Given the inferred age of Scarabaeinae as originating in the Lower Cretaceous(145-100mya) , the major radiation of dung feeders prior to the Cenomanian (100-95) mya) , and the early divergence of both African and Gondwanan lineages, we hypothesise that faunal exchange between Africa and Gondwanaland occurred during the earliest evolution of the Scarabaeinae. Therefore we propose that both Gondwanan vicariance and dispersal of African lineages is responsible for present day distribution of scarabaeine dung beetles and provide examples."(Gunter et al 2016)

While many dinosaurs were herbivores, a large amount of bone and numerous traces of soft tissue in their coprolites suggest that the food Tyrannosaurs ingested did not remain in their digestive systems long enough for all of it to break down, making their digestive systems unlike those of living crocodiles and snakes. Yet their digestive systems were enough to produce methane.

Presumably something comes in to do a primary breakdown. This is where the paleoscatologists come in. They have found dung-beetle burrows in dinosaur fossil faeces, from this period (Chin 2008). Again the tracks and burrows can often tell us more than body fossils.

French paleoscatlogist Marie-Antoinette De Lumley

Holometabolism

We have seen holometabolous insects 300-250 mya. But the big explosion in holometaboly was this period. Holometabolic insects in present times account for 60% of all animals having the body composed of cells differentiated into tissues and organs. They really come into their own between 150-100mya, and made big advances and diversified widely at this time. They began to take over from those insects that reach adulthood through a series of slight changes, through a number of ‘nymphal stages’. Now we have the wide emergence insects with distinct growing stages – eggs, larva pupa and adults - complete metamorphosis. The typical story within the Hemimetabola is for nymphs and adults to share similar morphologies, habitats and trophic needs. The stunning success of the Holometabola comes from its highly divergent stages because the life history splits into two major modules, the larva and adult. Each could evolve and adapt independently to exploit different niches for growth versus reproduction.

Aristotle

“Aristotle made important contributions to the study of developmental biology, including the complete metamorphosis of insects. One concept in particular, that of the perfect or complete state, underlies Aristotle's ideas about metamorphosis, the necessity of fertilization for embryonic development, and whether morphogenesis involves an autonomous process of self-assembly. Importantly, the philosopher erroneously views metamorphosis as a necessary developmental response to lack of previous fertilization of the female parent, a view that is intimately connected with his readiness to accept the idea of the spontaneous generation of life" (Reynolds 2019)

Other ideas

“The problem of insect metamorphosis has inspired naturalists for centuries. One question that often arises is why some insects, such as butterflies and bees, undergo a fairly radical metamorphosis while others, such as crickets and lice, do not. Even before the concept of homology emerged scientists speculated which stage found in ‘more direct-developing’ (nymphal) insects would correspond with the pupal stage of metamorphosing insects.

William Harvey (1651) considered the pupal stage to be a continuation of embryonic events, calling it a “second egg.” "Since then variations of this idea have emerged over the centuries of scientific research and have been supported by a wide variety of methods and rationales. This review will follow those ideas and the ideas that emerged in opposition to them to the present state of the field" (Erezyilmaz 2006)

Nymphal role?

By decoupling larval and adult development, larvae and adults were able to occupy separate ecological niches Also the internalisation of the developing wing primordia allowed burrowing of worm shaped larvae. So these juveniles were then able to live inside leaves, fruits and detritus, all of which there was a lot more of in this period.

So let’s have a closer look at those larvae. There have since been numerous ideas for how the larval and pupal stages of the Holometabola were derived from their hemimetabolous ancestors. (Truman & Riddiford 2019) Two views predominate. Boiled down the debate is between whether larvae came from early nymphal stages, or whether later nymphal stages became pupae.

Not just leaf fall

When those leaves fall, there will be all sorts of creatures on and in them which fall to ground too. I remember being startled by the number of different sorts of ladybirds appearing on picnic table beneath trees one autumn. Much of the nutrition derived from above would have fallen to earth.

There will be all sorts of aphids, along with the larvae of many beetles, butterflies, wasps and flies that fall to the ground. This may well be the time when some of those larvae found that going underground provided a rich source. Some insects, after falling off, may have returned to earth to lay their eggs, so that their larvae could grow up in the soil. Again we presume they have always been there, but they were not involved in the creation of the soil architecture. Instead they tend to disrupt it , but now could feed off the spoils of previous few millions worth of humification.

Insects can fall to earth in different stages of development. Some adult beetles feed on the leaves of plants, or nectar, then lay eggs into the surface soil in Spring, where their larvae grow up. Others like many butterflies and moths spend their adulthood looking for mates, while their larval stages crawl over leaves, then pupating in soil. There are all sorts of variations.

Mouthparts

Remember that it is the mouthparts that mainly distinguish insects (ectognathus) from the earlier hexapods like diprlurans and springtials with endognathus mouthparts "During the Cretaceous, three new mouthparts classes are added, yielding >97% of all insect mouthparts at the end of the period. Coleoptera Meloidae, Hymenoptera had maxillar-labial mouthparts, and Lepidoptera with elongate proboscis, were all associated with nectarivory. (Nel et al 2018)

Beetle (external parts) springtail no visible parts

Insect mouthparts have been structured to chew, pierce and suck, siphon, lap, sponge, bore, and mine on and within a wide variety of tissues, as well as filter, sieve, and collect particulate food such as plankton and pollen. " (Labandeira 2019)

These accounts concentrate on the adult mouthparts adapted for sucking nectar, but it is apparent that feeding in the adult stage played a minor role compared to feeding in the larval stages. Larvae are eating machines. They may be in the living plants, the dead parts of plants and animals, as well as the soil itself. All these new environments were being explored. Their mouthparts could probably tell us a lot, as different mouthparts eat different foods.

5 bursts

The evolution of insect mouthparts has taken place in five or six bursts, separated by intervals of rather static mouthpart morphology. Over 80% of these mouthparts had appeared by 200mya, but “During the Cretaceous, three new mouthparts classes are added, yielding 97% of all mouthparts at the end of the period” (Labandeira 2019). Found Myanmar amber are entirely novel, or unconventional combinations of characters from previous types, some once thought as extinct but reappearing after a hiatus of tens of millions of years.

“One of the fascinating aspects of Cretaceous ambers is that they record an outgoing insect fauna predominant during the Permian and early Mesozoic as well as an incoming insect fauna prevalent in the world today” Insects fossils in amber can tell us about mouthparts - but usually of adults stuck in amber. Such mouthparts were used to access vascular tissue, particularly more nutritious phloem rather than xylem.

Clearly these changes to mouthparts provide a massive advantage for holometabolism, especially when there are different habitats that can be exploited - the air, living plants and the litter/soil. We hear a lot about adult insects flying around looking for mates to have sex.

Trophic levels

“No other biological structure possessed by multicellular organisms is responsible for the wholesale transfer of energy from one trophic level to a superjacent trophic level than insect mouthparts." (Labandeira 2019). Insect mouthparts have been structured to chew, pierce and suck, siphon, lap, sponge, bore, and mine on and within a wide variety of tissues,

Did hemimetabolous insects emerge from the soil, while holometabolous insects fall from the sky? Their falling would lead to what I call 'terrestrialise'. Where many who use the word terrestrialise talk about a great leap, here it is more of a great fall. When they land, they inhabit the existing soil. They do not help construct it.

Most accounts of the dispersal of holometabolic insects concentrate on what was going on in the air between flying insects and flowers (coevolution). Below ground, despite the proliferation of leaf litter, only a few -like scarabs - eat decaying matter and dung. Most soil dwelling larvae, like wireworms, leather jackets & chafer grubs, target roots of living plants, where they now do a lot of agricultural damage.

They were massive in comparison with the oribatids and springtails, and several ground dwelling insects, like ants and rove beetles, could now survive by eating the smaller soil animals.

Cenozoic insects

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