Predation & parasitism of widows

Although widows are mighty predators, they are occasionally preyed upon by various animals. Some critters see widows as a quick and nutritious snack. The red mark/hourglass on the ventral abdomen serves as a warning to them that there is danger should they miss and get bitten. A significant chunk of widow death is attributed to parasitism by invertebrates.

Philolema latrodecti has been re-classified several times and will sometimes be referred to as Eurytoma latrodecti, or sometimes even Desantisca latrodecti. It has been observed that this species can and will parasitize different species of widows, mainly geometricus and mactans, although variolus and bishopi are also at risk. On average, 16 wasps emerge from a single egg sac.

Here is a size comparison of Philolema latrodecti:

Female & male:

This is an egg sac opened up, showing what it looks like inside:

Contents emptied:

Baeus latrodecti is the most efficient parasite of black widow spiders. Observation of several egg sacs showed that 98.55% of the (~3000 total) eggs were parasitized! The female cuts her way into the egg sac and parasitizes the eggs inside. She must oviposit separately in each egg. Not all egg sacs with holes in them mean that spiders emerged. If the sac is heavy, it is probably parasitized. Flies will emerge from the sac within seven days, and will immediately copulate.

Female (females of this species are wingless. Consequently, they have very long legs and are capable of jumping 65x their body height):

Male:

Egg sac with hole (again, hole does not always mean emerged spiderlings!):

Mud daubers will hunt out and sting a female widow spider, paralyzing her, only to drag her back to the nest to serve as food for her young.

Here a mud dauber has paralyzed a mactans and is in the process of taking the spider back to her nest:

Contents of a mud daubers nest (you can see many different spiders there, notice the Latro):

Pseudogaurax signata (may have been reclassified?) is an egg predator. The female will lay her eggs on the surface of the egg sac and the larvae must penetrate the sac and enter. Upon entering, they feed on the eggs inside. This species will not decimate the sac as Baeus does; the ratio of emerging spiderlings to flies is 5:1.

Gelis sp. (an Ichneumonid, from California) is a predator of Latrodectus in its larval stage.

Remember that "mighty predator" bit at the beginning? Yeah, they get their revenge on the wasps too: