Parasitoid Wasp Pupae on Tarbala Caterpillar

In the last blog I explained about Trabala Species of Lappet Moths. Few days back I found another Trabala caterpillar. This one was infested with pupae of Parasitoid wasps all over its body. It was lethargic and was unable to move.

In general though most people still use the term Parasitic Wasps. Technically speaking, they are not actually parasites – they are parasitoids. This is because a true parasite is something that lives at the expense of its host but doesn’t actually kill it, whereas parasitoids nearly always kill their host.

Parasitoid larvae usually develop by feeding on a single host – different species develop on anything from tiny aphids and insect eggs right up to large butterfly and moth larvae. They can live and feed inside the host’s body cavity (endoparasitoids) or outside the host’s body (ectoparasitoids). They can be solitary or gregarious – with anything from 1 to many 1000′s of larvae consuming the same host.

Parasitoid Wasp On Tarbala Closeup

Fascinating life strategies

Nearly all parasitica inject venom into their host along with or just prior to the egg. This venom is a highly complex mixture of chemicals and other agents used not just to paralyse the host, but to also modify the host’s tissues. Tissue modification is a feature of nearly all venoms, making the host more nutritious for the developing wasp larva and helping to overcome the host’s immune systems. The latter is an especially important consideration for internal parasitoids as a host’s body will usually try to surround (encapsulate) a foreign body to prevent infection and to kill any parasitoid eggs or larvae. Parasitica have developed many ways of getting around this but I think the most devious must be the use of polydnaviruses (also known as Poly-DNA-viruses) . These viruses are injected by some endoparasitoids with the venom and have been shown to target and disable the host’s immune system – thus protecting the developing parasitoid. Other, more basic, methods of bypassing the host’s immune system include laying the egg directly into the host’s brain (ganglion), where the immune system is unable to encapsulate it.

Whichever method the parasitoid uses to prevent encapsulation it must also protect itself against many other dangers. One of the most serious being the possibility that a host will succumb to a fungal or bacterial infection and die before the parasitoid has finished with it. To prevent this, many larvae secrete chemicals with antibiotic or antiseptic properties as they move around the host’s body cavity. They also avoid damaging the host’s gut (a massive source of bacteria) by eating non-essential areas first, like body fat and the reproductive organs. Many species also use teratocytes – bundles of cells that emerge from the egg with the embryo. These cells absorb food from the host’s body cavity and the parasitoid larva feeds on them – removing the need for it to feed directly on the host’s tissues until it is absolutely necessary.

Parasitoid Wasp Puape On Tarbala Caterpillar

Polyembryony is another complex strategy employed by parasitica, but this time its aim is to ensure the maximum number of offspring from the fewest number of eggs. Some species lay a single egg that continues to divide, cloning itself into many independent larvae – in extreme examples one egg can produce thousands of larvae. Some species have even been shown to produce different types of larvae from the same egg – normal larvae that feed and develop fully into adult wasps and others, which never mature into adult wasps, that act as guards to protect the others from attack by other parasitoid larvae.

Charles Darwin even used one family of Parasitoid wasps as evidence for natural selection, writing to a colleague:

I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.

So what next turn will you see in the story of lappet moths, wait for my last installment on 3 part series on Lappet moths.

Trabala Caterpillar Defensive Pose

Last year I found this caterpillar of Trabala Species of Lappet moth at Mangalore.

Lappet moth belongs to family of moths called Lasiocampidae. They are also known as eggars, snout moths. There are over 2000 species worldwide, and probably not all have been named or studied.

Their common name snout moths comes from their unique protruding mouth parts of some species that resemble a large nose. They are called lappet moths due to the decorative skin flaps found on the caterpillar’s prolegs.

Trabala Caterpillar Showing Prolegs

The name eggars comes from the neat egg-shaped cocoons of some species.

Caterpillars of this family are large in size and are most often hairy, especially on their sides. Most have skin flaps on their prolegs and a pair of dorsal glands on their abdomen. They feed on leaves of many different trees and shrubs and often use these same plants to camouflage their cocoons. Some species are called Tent caterpillars due to their habit of living together in nests spun of silk.

Trabala Caterpillar Closeup

As adults, the moths in this family are large bodied with broad wings and may still have the characteristic elongated mouth parts, or have reduced mouth parts and not feed as adults. They are either diurnal or nocturnal. Females lay a large number of eggs which are flat in appearance and either smooth or slightly pitted. In tent caterpillars, the eggs are deposited in masses and covered with a material that hardens in air. Females are generally larger and slower than the males, but the sexes otherwise resemble each other. Moths are typically brown or grey, with hairy legs and bodies.

Almost all stages these caterpillar are poisonous to human beings. Their hair results in urticarial rashes. When your skin brushes against these caterpillars, the spines break off, releasing an irritating fluid that produces an immediate stinging, burning sensation. The numbness and swelling that follow may extend to your whole arm or leg in severe cases. Red blotches may persist for a couple of days, accompanied by a weeping rash. Associated lymph nodes may swell and be tender for 12 to 24 hours. Systemic reactions may include nausea and vomiting.

If one affects you, treat the symptoms. To remove any spines still in the skin, gently stick a piece of adhesive tape to the site and then pull it away. Applying cold compresses can lessen the
pain and swelling. Pain medications and topical corticosteroid creams may help. If the symptoms include systemic reactions consult medical help.

You might be wondering why I am showing you this caterpillar which was an year old. There is a reason wait for my blog tomorrow for next installment of three part series on Lappet moths.