Parasitized Spider

I came across this one yesterday when I stopped to look at a curious web in the dead end-branches of a willow tree. It was about 6 feet off the ground and I saw a tangled web, about 5 inches diameter, with a brown spider in the center. I'm thinking, "Theridiidae of some kind."

A closer look revealed a spider with a parasitic larva on its abdomen! I believe now that the spider was an araneid, and the tangled web was the result of chemical "instructions" it received from the larva. My understanding is that after the spider is initially parasitized, it goes through it's normal life cycle of building orb webs, trapping food, etc. Then, when the larve reaches a certain size, or age, or point in its development it injects a chemical into the spider which causes the spider to spin this uncharacteristic web - which, in reality, is a protective web in which the larva can finish consuming the spider and safely pupate.

Anyway, I took some pictures, but in my excitment I forgot to take whole-web pictures (Arrgghhh!). I did get a closeup of the pair in the web, which includes some interesting star-like patterns of threads (see later picture).

I collected them and took some more pics under the scope. It's a good thing I did, because just a couple of hours later the larva finished eating the spider's abdomen and started to pupate. It completed its pupation during the night. I have it in a covered petri dish and will take pictures of whatever energes.

I believe I came upon the spider/parasite pair shortly after the spider finished building its "death web," since the larva didn't take long after that to finish eating it.

So, here are some pictures of this interesting event:

Spider and parasite in the "death web":



Part of the death web, showing cluster of threads within the web, radiating from a central point:



Head of larva at top:



A couple of hours later. Not much left of the spider's abdomen:



The pupa is about 5 mm long:

very cool jsloan. interested to see what comes out.

very interesting, thank you for sharing.

can't wait to see what comes out!

very cool. can't wait to see it. nice find.

that is sooooooo cool.

Cool

Thanks for sharing this. I didn't realize some insects had such advanced ways of parasiting. I see the grub got obviously darker in the later pic after it's ingested most of the spider. I'm gonna guess wasp, anyone else going to take a guess before we see what comes out?

looks like your on to something

Here's something I didn't expect. The pupa has expelled what look like feces (taken about 3 days after pupation). I thought pupae were a kind of "dormant" period while the body rearranges itself. Apparently, that isn't so.

Of course, the larva had recently finished what is probably the biggest meal of its life, so naturally ... :razz:

BTW, I looked at the other end of the pupa this morning, through the microscope, and saw some movement in there. Something dark, perhaps the head of whatever will be coming out.

interesting. i guess the pupa phase is a little different for every critter.

Very intresting. I think it's gonna be a wasp.

We're waiting...

Fascinating! Please be an eight legged wasp with peds... XD

Whatever it is don't let it escape and get to your spiders...!

Yeah...

Yeah... just before I posted I would've bet 'mantis fly' but then I remembered from another forum that they spawn from spider eggsacs they've parasitized (real word?). It could still be a fly, could even be moth - grub kind of looked like one. Still betting on wasp since my second guesses tend to be wrong.
X-D

Keep us posted! I'd love to know whats in there. I'm guessing a wasp as well.

luckie_couture said:

Keep us posted! I'd love to know whats in there. I'm guessing a wasp as well.

Click to expand...

Will do. It's been just over 7 days now since pupation, but nothing has emerged yet. I'm hoping to see something soon.

The pupa has hatched! Late this evening I found what looks like a wasp in the container. It emerged sometime today, the 8th day after pupation. Here are some hurried pictures I just took of it. I have it in a covered petri dish, and took the pictures through the cover whenever it stood still long enough for me to get a shot.

BL = 5mm long (not counting the antennae, which are about as long as the body).

Does it look familiar to anyone? I'm not up on my wasps.

Dorsal view:



Ventral view, focusing on cephalothorax and head:



Ventral view, focusing on the abdomen:

Dipogon species?

The wasp died, but in doing so left itself in an excellent position for seeing more structure: wings straight out, legs out, antennae out. I couldn't have mounted it better than it ended up!

So, here are some more pictures:

Dorsal view:



Ventral view:



Closeup of right-side wings, dorsal view: