Hogna radiata is a species of wolf spider that is common in Southern Europe. Females are pretty much confining themselves to the immediate neighbourhood of their abode, while the males are more prone to roam about.
Yesterday I found four drowned males in a water-filled plastic container that I had left out on the meadow in an attempt to salvage a water plant (no luck, it’s dead, too). Inside the container were two more males, wet but alive, that seemed unable to get out on their own. I helped them out, poured out the water, but discovered that there was movement at the bottom: dragonfly larvae! So off I trotted to get some water for the larvae… When I came back, I found yet another male Hogna radiata sitting inside the container.
While I think I can understand that spider’s behaviour (he may have been attracted by the larvae moving about frantically searching to reach the wettest part of the container), I couldn’t quite understand the ‘mass’ suicide. I had never come across so many males in one spot, and was wondering why they would venture in water so deep for them to drown in. How did they even realize there was something edible in that container? Wolf spiders have good eyesight, ok, but the container wasn’t see-through.
Early this morning I noticed two more male Hogna radiata hanging out where there was water at the bottom of containers. I had left black mortar containers leaning upright against a fence to gas out (they stink disgustingly when they’re new), and some rainwater had collected at the bottom along the edge, perhaps 1 or 2 cm deep. Again, the spiders were sitting on the wall very close to the surface of the water.
Some wasp spiders (Argiope bruennichi) had built their webs across the opening of the containers, and there were plenty of insects of all sizes flitting in and out, some ending up in the webs. This time of year there are also loads of small grashopper nymphs around, and they don’t seem to have much control of where they’re jumping.
Watching the Hogna radiata males I wondered whether hunting close to water was easier for them, as their preys were already having a hard time getting out of the water if they happened to end up in there, so for the spiders it would be like visiting a restaurant. I haven’t however actually SEEN any of those spiders catch a prey or even trying to, so I have no way of knowing if what they are/were doing there by the water was food-related at all.
I’d love to find out more about their motives. :-) Can anyone here help?