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Insects
Insects
Due to the dry climate, the interior of Pangaea was mostly desert and at higher latitudes, gymnosperms survived and conifer forests began to recover from the EPE well as the newer groups of beetles. The only new insect group of the Triassic was the grasshoppers.
This may give the impression that nothing much happened in insect evolution. Yet it was in this period that the foundation for future developments were built. The key development - the development of wings in adults - seems to depend on the other part of their life cycle (larvae) developing - in soil.
Please read in conjunction with
Together, these show how the environment of the soil affected these creatures and enabled the evolution of key insect characteristics, particualry flight.
Many of the early orders of insects developed during the previous Permian period became extinct. The aftermath of the end-Permian extinction (EPE) provided new ecological niches and opportunities for surviving and newly evolving organisms, The survivors of EPE event evolved in this period to what we consider the modern insect orders that persist to this day. Most modern insect families appeared in the period, but many radiated (ie evolved into various groups) much later, like the flies and beetles.
Oldest families
Oldest families
Some of the oldest living families, that we see today, appear during the Triassic. Hemiptera included the Cercopidae, the Cicadellidae, the Cixiidae, and the Membracidae. Coleoptera included the Carabidae, the Staphylinidae, and the Trachypachidae. Hymenoptera included the Xyelidae. Diptera included the Anisopodidae, the Chironomidae, and the Tipulidae. The first Thysanoptera appeared as well.
Wasps
Wasps
Wasps and sawflies belong to the Hymenoptera and emerged during this period (Peters et al., 2017). The family tree (phylogeny) of this order seems quite clear. The sawflies came first, "This is a very primitive group – dating back 250 million years ago to the Triassic – and the majority (true sawflies, the Tenthredinoidea) are all herbivores, feeding on the foliage of many different plants, although one group (Orussoidea) are external parasites of wood boring beetles." Sawfly larvae eat tons of leaves.
They developed a waist to become wasps, often parasites, with their relatives the ants not appearing until the next period and bees not for another 100 million years. I can’t see how the early Hymenoptera would have contributed to soil development. Wasps tend to make nests for their larvae.
Beetles
Beetles
Permian xylophagous (wood boring) beetles suffered a severe extinction during the EPE largely due to the collapse of forest ecosystems, resulting in an Early Triassic gap of xylophagous beetles. New xylophagous beetles appeared widely in the early Middle Triassic, which is consistent with the restoration of forest ecosystems
These beetles, but more especially flies, took off in this period - thanks to the soil. Their larvae found enough to eat in the soil to produce the flying adults, which rarely eat much. Some of the present-day versions are considered pests because they eat valuable crops. It gives you an idea of what they may have been eating then.
Adaptability
Adaptability
Beetles were highly adaptable and resilient, and able to diversify into these new niches. The reduced competition and the availability of new resources allowed for rapid adaptive radiation, where beetles evolution, leading to the emergence of new families and subfamilies. Post- EPE saw significant changes in climate and vegetation, which influenced the evolution of herbivorous beetles like scarabs, as well as predatory and decomposer beetles like staphylinids and elaterids. The recovery period after the EPE was a critical time that set the stage for the rich variety of beetle families we see today. Many evolved a hundred million years later.
During the Late Triassic, mycetophagous, or fungus feeding (i.e., Cupedidae) and algophagous, or algae feeding species (i.e., Triaplidae and Hydrophilidae) of beetle begin to appear.. The first primitive weevils appear (i.e., Obrienidae), as well as the first representatives of the rove beetles (i.e., Staphylinidae)..
Bugs
Bugs
The first true bugs (Hemiptera) had developed in the previous period. One true bug is the cicada and this evolved around 220-200mya. It is possibly the most famous insect that spends most of its life in soil. It emerges once every 13 or 17 years to take flight, often creating clouds of cicada. This hemimetabolous insect spends all that time going through various nymphal (rather than larva) stages to eventually emerge as a flying adult.
Grasshoppers
Grasshoppers
Grasshoppers evolved at the start of this period. They are typically ground-dwelling insects with powerful hind legs which allow them to escape from threats by leaping vigorously. It is ahemimetabolous insects, so go from an egg into a nymph or "hopper" which undergoes five moults, becoming more similar to the adult insect at each developmental stage. At high population densities and under certain environmental conditions, some grasshopper species can change color and behavior and form swarms. Under these circumstances, they are known as locusts.
The earliest insects that are certainly form of grasshoppers called Caeliferans are now extinct, but date from the early Triassic, roughly 250 million years ago. The group diversified during the Triassic and have remained important plant-eaters from that time to now.
Rove beetles (Staphylinids)
Rove beetles (Staphylinids)
The oldest recorded staphylinid, more than 200 million years old, is from the upper Triassic of the USA. Staphylinidae is the largest family in the U.K. as well as in many other European countries, and it is more than 4000 species in North America. The feeding habits of staphs are similarly diverse but in a very general sense the four groups tend to specialize in various ways; fungi, and especially decaying fruiting bodies, while the larger ones on the abundant insect larvae, particularly those of various Diptera. Many species develop in temporary habitats e.g. decaying plant and animal or fungal matter, dung or by temporary pools, and so, in general, the immature stages tend to grow rapidly, in days or weeks, while the adults tend to be long-lived
Do you think?
The rove beetle larvae (left) look like small soil arthropods - eg diplurans (right). When they went and walked on to the surface they breathed that XS oxygen to make them bigger.
Dipluran - Japyx. 6-legged with similar segmentation. A predator that burrows and lays in wait for prey since 350mya - 100m previously.
However the size doesnt fit as larva 10X size of Diplurans..dis oxygen have an effect?
This adult looks v. similar to the larvae, except with stronger cuticle some flaps. Those flaps may be the first flight structures
As they came out of the soil, the 6-legged creatures did not need internal (endo) mouthparts to protect when eating so they are now exposed - ectognatha, a key insect characteristic
Soil dwelling Larvae
Soil dwelling Larvae
This is when insects took to the soil - well their larvae did. There must have been enough soil for these relatively large (compared with soil mites and springtails) creatures to live.These larvae are bigger than the existing soil animals, and they may use existing cracks and tunnels rather than pores to live. The insect larvae and grubs do not use the existing pathways, instead burrowing in.
Many soil dwelling larvae spend years underground before hatching. It is easy to see why there are so successful – providing about ¾ of all know species of creatures. The adults can disperse easily with the wings, while the larvae are protected from predators – although birds like to eat these bigger soil creatures. They have been pests in farming for centuries, and even with the chemical pesticides many insect larvae are still difficult to control.
These soil dwelling larvae do not fit the existing soil architecture, instead they bulldoze their way through.
The beetle and fly grubs would be a good source of food for predators, as we see today when birds peck them out of the fields or lawns. But then, of course, there were no birds. But neither were there any grasses or carrots. Did they go on to these roots becoming ‘pests’ later? The distribution of the Psilids – only in the Northern hemisphere - points to a later root invasion after Pangea split up.
We take it for granted some insect larvae eat roots, as many are now considered ‘pests’ – ie they damage crops. But they are probably the first creatures in earth to do so. Up till then the arthropods lived round the roots. The larvae is an eating machine. The adult is there to disperse, mate and lay eggs. Once winged insects had evolved from out of the soil, they could colonise many habitats. Adults could disperse far and wide. Some would find that laying their eggs in soils provided the larvae with now sources of food. Once early soils had formed, there would be a rich abundance of food as decomposed material would be a good source of nutrients, yet to be exploited.
Click Beetles (Elateridae)
Click Beetles (Elateridae)
"The data on the fossil generic diversity suggest that Elateridae originated in the Triassic and rapidly diversified and became comparatively abundant through the Jurassic. " Kundrata et al 2020)
Click beetles lay their eggs in soil where they emerge as larvae - called wireworms - which grow underground for several years sometimes considered a pest as they can damage grass fields and crops as the vast majority eat the roots of cereal plants and root crops such as carrot and potato. Click beetles like to stay close to the surface while other adults will spread themselves widely, and are called 'click' because they click out of your fingers - or beak if you were a bird.
Weevils
Weevils
The suborder Polyphaga, which includes weevils, is believed to have originated in the Triassic period, around 240 million years ago, but diversifies widely a 100 million years later. Their larvae live in soil. A particular pest in garden centres in Europe is the Vine weevil larvae (hatching out). It is a beetle that occurs as females only in northern Europe and they reproduce asexually. Their larval bodies are only slightly curved and they have no legs. They are up to 11mm long and like living in soil in pots – hence their pest status in garden centres.
Flies
Flies
‘True’ flies are 2-winged insects (Diptera) are known from the Middle Triassic, becoming widespread during the Middle and Late Triassic . A single large wing from a species of Diptera in the Triassic (10 mm instead of usual 2–6 mm) was found in Australia (Mt. Crosby). This family Tilliardipteridae, has numerous 'tipuloid' features. Tipulids also appeared in the Triassic. Known here as 'Daddy Long Legs' they have many other common names.
The larvae of craneflies (daddy long legs), (Diptera Tipulid) become the eating part of the life history, and spend many years underground. The larva of crane flies – leatherjackets can be a pest in fields and lawns. The female fly lays up to 300 eggs in your lawn in late-summer. These hatch after a couple of weeks into grey-black, legless larvae that have a tough, leathery skin, hence the name ‘leatherjacket’. From autumn through to summer, the larvae feed on the roots of plants, eventually growing to 5cm in length before pupating and emerging as adult flies in late-summer. Grass growth slows down and yellow, dying patches appear in the lawn. Dead and dying grass can be easily pulled up to reveal little or no root growth
Leatherjacket above, larvae of
Crane fly below
Rust flies, belonging to Psilid family are common in Northern temperate zones. Their larvae live either in stems, tubers, or roots and a few species under tree bark. Several are now common pests including the carrot root fly. The adults lay their eggs from May near susceptible plants, which hatch into white maggots, which tunnel into the roots and feed there in mid-summer when they pupate and hatch into the second generation. With the development of new root-based crops, they can cause extensive damage to carrots, celery, parsnips and parsley.
Holometabolous Insects
Holometabolous Insects
The earliest holometabolus insects emerged in this period and were probably the Megaloptera (large clumsy wings) . “Megaloptera is arguably the oldest extant clade of Holometabola. Megaloptera belong to a large monophyletic group, the Neuropteroidea, together with Coleoptera (beetles), Strepsiptera, Raphidioptera, and Neuroptera...We see the adults rarely as alderflies Dobson flies and fishflies. All species of Megaloptera have aquatic larvae, whereas eggs, pupae, and adults of all species are terrestrial. Is arguably the oldest extant clade of Holometabola …since about 230Ma.” (Gasperín 2019)
One origin?
One origin?
Holometaboly is extremely successful, as these insects make 60% of all animal species. Complete metamorphosis, which seems to have originated only once in insects, appears to have been almost fully retained, although also it has also restrained the body plan.
For many years we learned about Haeckel's famous 'law of recapitulation'. This proposed that when developing from egg to adult, animals ‘recapitulate’ successive stages in evolution – that ‘ontogeny’ recapitulates ‘phylogeny’ (McMahon and Hayward, 2016). This has since been discredited – that there is no precedent in the family tree for this sort of development.
Homometaboly developing
Homometaboly developing
Did the holometabous life cycle develop in water, then some larvae went into the land – they could now ‘land’, as there was something to live in. Basically they could loose their appendages and become more wormlike.
There is a lot of scientific argument about the relation of hemimetabolous and holometabolous insects. I would like to posit that hemimetabolous insects emerged through a series of nymphal forms from the soil, while holometabolous insects came back to the soil in a completely different form. Now there was soil, ready to be invaded, it opened up new ecological niches The plants started growing well after a few million years after the great extinction, and soil decomposing the debris so creating new ecological niches – that larval forms could exploit.
More modern opinions still oscillate between the two conceptions of the hemi- to holometabolan evolutionary trend and how they came about. But none discuss the role of the soil in this process, yet it must have been crucial in their development.
Hemimetabolous insects developed and grew THROUGH soils, while holometabolous insects came BACK to soils. Their eggs would have to be fertilised before being laid in soil, unlike existing soil creatures, many of which leave their eggs to be fertilised. Midway through this period, there was enough rich soil for creatures to live in. It was structured and could be pushed by strong creatures. Worms can push soil out of the way, so too can insect larvae. They could eat roots and fungi.
The selective advantage of complete metamorphosis (holometaboly) is that within one species the two forms with different lifestyles can exploit diverse habitats. The adults exploit the air- at that period – without competition or possible predation. The larvae can chew their way through leaves or the roots in comparative safety.
While holometaboly in insects first appeared 100 million years previously, it was in this period that these creatures really took off. Literally.
Wings
Wings
We saw the early development of holometabolous insects 50 million years previously, mainly well protected beetles, running around, rather than flying around. The holometabolous insects expanded dramatically in this Triassic period. that nowadays account for over 60% of all animal species. They could live part of their lives protected in soil, and the other part as adult flying around. The new airy environment had loads of plants to eat.
Abominable mystery
Abominable mystery
“Pterygota, the winged insects, are indisputably monophyletic. It is between the silverfish-like common ancestor of Dicondylia and Pterygota that the first flyer appeared. While the functional morphology of the insect wing is robustly understood, the more abominable mystery has been the origin of the structure itself. Flight is ancient and insects took to the air not long after arthropods invaded land. (Engel, 2015)
AND
What came first – the flying insect adult or the fertilised egg in the soil?
With the explosion of insects taking to the air some to feed, some to have sex. While the adults flew about their larvae found new places to eat. Many ate plants either above ground or below in the soil. The energy to make the wings to enable flight - for insects – comes from plants and the soil originally. Once the creatures had crawled out and taken to the wing, as insects do, they could colonise other habitats, now including a much richer soil
Ptera = wing
Ptera = wing
There was an explosion of flying insects – sawflies, wasps and flies spent much of their time on the wing. Insects are characterised are classified by their wings. Their wings (or ‘ptera’) determine the various ‘orders’ of insects. So flies are Diptera (2-winged) and beetles Coleoptera - hard wings. The ‘primitive’ mayflies are Ephemeroptera 'to live but a day'
There is lots of debate – again - about whether and how these groups developed – whether from one stock (as above) or many. The Hymenoptera, wasps and sawflies, and Diptera (flies) took to the air first. Lepidoptera (Butterflies & moths) took off later.
This is where the word ‘terrestrialisation’ is appropriate. The flying insects are coming back to earth, laying their eggs and their larvae developing in the soil, in a world that offers new opportunities. While the soil web is saturated with springtails and oribatids, these larvae go for the roots of plants.
Cerylonid
Cucujoidea
Chrysomelidea
Curculionoida
Elateridae
Bostrichiformia
Scarabaeiform
Polyphaga
Hydradephaga
Fg 1
Check out how many of these beetles would have had soil dwelling larvae
Chrysomelid - adults overwinter in soil
Curculin - weevils - vine have soil larave
Elateridae - yes wireworms
Bostrich - wood boring
Scarab - inc chafers (Melolontha) - which have bug white grubs i soil
Polyphaga - vine weevils
Cerylonid
Cucujoidea
Chrysomelidea
Curculionoida
Elateridae
Bostrichiformia
Scarabaeiform
Polyphaga
Hydradephaga
We see take-off among insects with the adults flying around what would have been a new aerial environment then. Increasingly they had trees and other plants, that offered new sources of food. Soils to these holometabolous insects is a secondary adaptation, rather than primary as with more primitive hemi-metabolous insects.
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