Insects of week: A Tale of Two Parasites

This week we profile two parasites, one that “attacks” after nests are completed and one that “attacks” as the nests are being made or even before nest construction begins.

A female Leucospis affinis ovipositing through completed nest plug in block 131068

A female Leucospis affinis ovipositing through completed nest plug in block 131068

Scientific nameLeucospis affinis

Common name: Giant Chalcidoid wasps

Family: Leucospidae

Nest type: parasitizes available larvae usually Megachilidae

Size: 7 to 12 mm

Nest tunnels used: parasitizes any available tunnel

Looks like: a smooth bodied, black and yellow wasp, females have a bulbous abdomen (ovipositor wraps over it)

These parasitic wasps may seem brutal particularly to the Megachilidae that serve as their primary hosts. The way they parasitize is straight out of Saw. First, females drill through the walls or the plug with her ovipositor—can you imagine anything more Viking-like?—which is why when we make the bee blocks we are careful to not drill too close to the edge of the block. (If we do, then we raise lots of Leucospis affinis rather than the bees we love.) Getting through doesn’t take long as her ovipositor is long, pointed, and perfectly suited for the job. She lays her egg and then moves on to the next cell in the nest, repeating the process until the entire nest is parasitized. Check out the video below to see this amazing behavior in action:

After the larvae hatch, their mission is to seek and destroy. Not only do they attach themselves to their unfortunate hosts, eventually sucking them dry, they first hunt down other Leucospis larvae to clear out any competition. They grow up very quickly, leaving the nest as adults in as little as a few weeks. Nothing like a big meal to give a big boost.


A bee fly hovers in front of a nesting tunnel in block 141038.

A bee fly hovers in front of a nesting tunnel in block 141038.

Scientific name: Anthrax sp.

Common name: Bee flies

Family: Bombyliidae

Nest type: Any and all

Size: 7 to 14 mm

Nest tunnels used: Generalist parasite of wood nesting bees and wasps

Looks like: A fly with large, black-spotted wings

A bee’s nest should be its castle, but as we’ve seen time and time again, there are parasites and predators waiting at every turn to take advantage of the precious nest and nectar. Anthrax are of this opportunistic ilk. Much like the cuckoo bees Coelioxys, the bee fly Anthrax hovers around a potential nest and waits for the prime moment to lay her eggs. She can wait relatively undetected, but once the “rightful” owners leave to forage, she swoops in and shoots her eggs into the tunnel of her choice. Below you can see a video of a female in action:

Each fly larva feeds on a fully grown bee (or wasp) larva, then pupates. The Anthrax pupa bears a spectacular crown of spines. These spines help the pupa wriggle out through the nest plug made of mud, leaves or resin and to the freedom of the outside world.

Additional information:

This entry was posted in 2014, Insect of the Week, Uncategorized. Bookmark the permalink.

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