Parasitoid & Predator Field Manual: Identifying Tachinids, Braconid Wasps & Defense

Parasites vs. Parasitoids: The Ecological Distinction

Why parasitoids always kill their host

In biological terminology, a true parasite (like a flea or tick) lives off its host without intentionally killing it. A parasitoid, by contrast, is an organism whose larvae develop inside or on the host body, consuming its fat reserves and hemolymph non-lethally before finally consuming vital organs and killing the host at maturity.

In nature, parasitoid flies and micro-wasps serve as vital biological regulators preventing insect overpopulation. However, in a captive rearing enclosure, a single undetected parasitoid can multiply and infect every caterpillar in the habitat.

Tachinid Fly Identification & Egg Removal Technique

Lespesia archippivora and the telltale "white sesame seed" eggs

Tachinid flies (especially Lespesia archippivora) resemble standard household flies with bristly abdomens. The adult female hovers over caterpillars, gluing microscopic, oval white eggs—resembling tiny sesame seeds—directly behind the caterpillar head capsule or along thoracic spiracles where the caterpillar cannot groom them off.

Once laid, the fly maggot hatches within 24 to 48 hours, drilling directly through the caterpillar cuticle into the body cavity. It feeds on non-vital fat bodies until the caterpillar attempts to pupate into a J-hang, at which point the maggots emerge on white silk-like slime threads and drop to the bottom to pupate into brown, pill-shaped puparia.

Braconid Wasps (Cotesia) and White Silk Cocoons

How endoparasitic micro-wasps manipulate host behavior

Braconid wasps (such as Cotesia glomerata and Cotesia congregata) are tiny micro-wasps measuring just 2 to 3 mm in length. The female uses a needle-like ovipositor to inject dozens of microscopic eggs along with symbiotic polydnaviruses that disable the caterpillar’s immune defense.

The wasp larvae consume the caterpillar from the inside over 10 to 14 days. When fully grown, they chew through the caterpillar’s skin simultaneously and immediately spin small, white, cottony silk cocoons on the caterpillar exterior.

Astonishingly, viral neurochemicals cause the dying caterpillar to act as a zombie bodyguard, aggressively thrashing its head to protect the wasp cocoons from other predators.

Chalcid & Pteromalid Chrysalis Wasps

Pteromalus puparum: The chrysalis destroyer

While Tachinids and Braconids target caterpillars, Pteromalid wasps (notably Pteromalus puparum) specifically attack freshly formed, soft chrysalises. The wasp is 2mm to 3mm long and metallic green or black, small enough to be missed entirely, and it works within the first 24 hours of pupation while the cuticle is still soft. A single female can lay up to 200 eggs inside one chrysalis.

The chrysalis hardens prematurely, turns dull chalky grey-brown, and never develops wing patterns. Several weeks later hundreds of pinhead-sized wasps chew 1mm circular exit holes through the shell.

Enclosure Mesh Sizing Standards: Why Standard Window Screens Fail

Micro-wasps easily pass through 16-mesh patio screening

A widespread beginner mistake is using repurposed window screens or standard patio enclosures. Standard window mesh is 16x18 mesh (holes are 1.2 mm wide)—large enough for tiny Chalcid and Braconid wasps to fly straight through.

Professional lepidopterists mandate 50-mesh fine polyester mesh (apertures under 0.3 mm) for all rearing enclosures. Fine mesh completely excludes micro-wasps, fungus gnats, and spider mites while still allowing 80% cross-ventilation.

Strict Quarantine & Humane Euthanasia Protocols

Preventing parasitoid spread across your sanctuary

1. Quarantine of New Finds: wild-collected caterpillars are kept apart from captive-hatched ones for about 7 days rather than going straight into an established habitat. A parasitoid already inside a wild caterpillar is invisible until it emerges, and by then it is in the enclosure.

2. Parasitoid Disposal: where Braconid cocoons or Tachinid maggots appear, the container comes out at once and the parasitoids go into a sealed zip-top bag in the freezer for 48 hours. Left in place, they emerge and parasitize the rest of the brood.

3. Humane Euthanasia: after extensive internal parasitoid emergence, the usual method is an hour in a small container in the refrigerator to induce torpor, then 24 hours in the freezer. Chilling before freezing is the standard sequence for invertebrates, because torpor sets in before the cold becomes lethal.

4. Cage Sanitation Between Broods: 70% rubbing alcohol does not denature viral polyhedra or OE spore coats. The standard is a 10% sodium hypochlorite solution — 1 part household bleach to 9 parts water — with a 20-minute soak.