A Monster at the Stream

When I was out collecting aquatic insects with my girlfriends a few weeks ago, I looked up at one point and realized one of our team wasn’t with the rest of us, the ichthyologist. A few minutes later she came hurrying up the stream, asking where she could find a bug net and muttering about something “enormous” as she zipped past the rest of the group. She rushed back downstream and didn’t reappear right away, so I figured she’d missed out on whatever prize she was hoping to bag with the net. It happens. A lot. But she eventually came trudging back up the stream, net carefully folded over in her hand, and a big smile on her face. She said she’d found something amazing and wanted to know if the rest of us, all entomologists, knew what it was. Then she handed over the net and we saw this amazing beast for the first time:

Campsomeris ephippium

Now, I didn’t take the photo with anything that gives you a sense of how big this thing is, but it is far and away one of the biggest wasps I’ve ever seen. I live in the land of tarantula hawks, so it’s not unusual to see some monster wasp flying about noisily through the air. I’ve seen a lot of big wasps, some positively enormous. I’d never seen one like the wasp my friend caught along the stream, but it was impressive even by my high standards.

The size alone was enough to make us all think the wasp was the coolest wasp ever, but there were two other characteristics that added to the excitement. One was the mouthparts:

Campsomeris ephippium

Those things look positively vicious! When we saw them, we all worried a bit that it might be able to chew its way out of the net as we looked at it, or that putting it into a plastic Whirl Pac (a type of medical specimen bag that is popular for work with aquatics) just wasn’t going to keep it contained. We eventually transferred it to a hard plastic sample vial for transport back to town, just to be safe.

The other thing I really liked about this wasps was the color. Just look at the bright orange against the black:

Campsomeris ephippium

Gorgeous! This was a seriously scary looking wasp, but incredibly beautiful as well. A really excellent find as far as I was concerned! We looked it up in a field guide when we got back to the car and learned that it was a member of the wasp family Scoliidae, a type of parasitic wasp, and I later IDed it to the species Campsomeris ephippium. I’ll come back to the biology of these guys in a moment.

I really wanted to photograph the wasp before my friend added it to her collection because it was one of the most impressive things I’ve seen recently. I set up my little white box, got all my flashes ready, and put the wasp inside. It immediately started flying around. It was obviously attracted to light, so it kept trying to fly out of the front of the white box straight toward my face. I can safely say that having a wasp this gigantic coming for your nose is more than a little scary! I wrangled the wasp into a bowl to try to calm it down and modified my white box with some spare nylon netting I had lying around so the wasp couldn’t get out of the box as I shot it.

Campsomeris ephippium

Then I waited for the wasp to calm down. And waited. And waited some more. It FINALLY calmed down about 3 hours after dark, a good 7+ hours after I put it in the bowl, so I carefully removed the bowl from the white box and started shooting. The flashes woke it right back up and it started flying around the white box, once again kept trying to come out the front. The netting kept the wasp contained inside the box, but this thing was a beast to photograph! At one point it landed on top of the flash right as I clicked the shutter release, drowning the wasp in bright light. That was pretty much that. The wasp fell absolutely in love with the flash and wouldn’t leave it alone the rest of the photo shoot. All in all, this wasp was one of the most challenging insects I’ve ever tried to photograph. What a frustrating little animal to work with!

But look how beautiful this animal is! The texture on the head is amazing:

Campsomeris ephippium

And all that hair! And those enormously thick antennae! I love this wasp!

So back to the scientific part of this post. I can’t just photograph some unknown insect this impressive without looking into it a bit more. Here’s what I learned about scoliids. I’ve already said they’re parasites, but they’re a specific type of parasite. They’re external parasites of beetle larvae, particularly scarabs. The females apparently burrow into the ground and find the c-shaped scarab grubs, sting them to paralyze them, then burrow even deeper into the ground before constructing a sort of cell for the now immobilized grub. Then she lays her eggs around the grub. The developing wasp larvae consume the beetle grub as they develop. Seems a properly gruesome mode of reproduction for a giant wasp! What’s even more amazing is they’ll often sting grubs, then decide they don’t want to use them and leave them behind. These grubs usually don’t fare so well and eventually die without developing further.

I also learned that these are likely a parasite of one of my favorite beetles, my June bug Cotinis mutabilis: