Centipedes, Millipedes, and Spiders, Oh My! - 1 September 2023

Leader Ben Klementz displays a vial full of pseudoscorpions!

​On the evening of Friday September 1st, arachnid specialist Ben Klementz led a group of 18 of us on a search for the Preserve’s many many-legged inhabitants. Ben is a PhD student in the Prashant Sharma Lab studying arachnid evolution and shared with us his deep interest in spiders, harvestmen (daddy longlegs), mites, ticks, and psuedoscorpions. What is a pseudoscorpion? To demonstrate, Ben had brought some specimens from his lab. We’d normally be able to find them out in the Preserve’s damp leaf litter, but it’s been a very dry summer. Preserved in alcohol, Ben introduced us all to the pseudoscorpion. They are pudgy little creatures with two scorpion-like pincer arms. While the pseudoscorpion does not have fangs like spiders and does not have a tail like a scorpion, it does have a venom gland located in its pincers! Fascinatingly terrifying. Though, to be fair, three of these critters could fit comfortably on your pinky nail, so they are no danger to humans. Just an important member of our native ecological community.

Next, Ben produced preserved millipede specimens. Millipedes and centipedes are not arachnids, but Ben maintains a fondness for them. Millipedes often smell like almonds, he said, because they are producing hydrogen cyanide in self defense. Be careful to not eat any millipedes that smell like almonds! Female spiders do not have any similar reservations about eating their mates. When a male spider approaches a female, it sends very specific vibrations through her web. These vibrations allow the female to discern the male from other prey, but then she has a choice. Female spiders will encounter many males throughout their multi-year lifespan, and so they can be choosy with who they mate with and who they don’t. Either way, the male ends up as food to ensure the female has enough energy for her eggs - whether those eggs were fertilized by him or not.

​

Specimens from the lab

The first spiders we encountered were Agelenid funnel-weaver spiders in the joints of the Picnic Point entrance fence. Unlike other web-weaving spiders, funnel-weavers do not add glue to their webs. These spiders instead use their speed to dart out and grab any prey that touches their web lines. Orb weavers and sheet-web weavers, on the other hand, do use glue. Spider silk glue is a fascinating substance that acts like a non-newtonian fluid, Ben informed us. Similarly to cornstarch and water, when an insect traveling at high enough speed hits the glue, the glue acts like a solid and the insect bounces off. When an insect traveling at the right speed hits the web, the glue acts as a liquid and captures them. Different spiders use different formulations of glue that speed-select their preferred prey, while preventing fast, dangerous insects like wasps from getting stuck. Silk glue chemistry also allows for the glue to be effective in wet and humid conditions, unlike most human adhesives.

The most common orb weaver we encountered was the furrow spider, named after a furrow that runs down the top of its abdomen. We even had the opportunity to watch some of these furrow spiders building their beautiful webs. Web-building spiders use their own body proportions to precisely measure out the spacing of their web strands, allowing them to make such amazingly complex-yet-standard webs in a variety of places. It turns out that the spiders that have taken up residence behind my car’s side mirrors are also furrow spiders! How they can make webs between my mirrors and doors that withstand highway speeds mystifies me. 

We also encountered a number of sheet-web spiders, which make more abstract net-like webs than the typical circular “orb” webs of their counterparts. Additionally, we spotted two harvestmen (or daddy longlegs) on the trip. These arachnids are not spiders, do not make webs, and only have one body segment. Ben was able to identify one as being a juvenile of an introduced European species. We found very few ground-dwelling arachnids like harvestmen, wandering spiders, and pseudoscorpions likely because of the dry conditions, though we did find one millipede!

Sheet web weaving spider of undetermined species found on swamp white oak.

As the sun set and it grew darker along the paved path up towards the Biocore Prairie, the spider webs became much easier to spot in the beams of our lights. We saw tiny intricate webs between leaves and huge multi-foot webs that were strung from sturdy ground anchors. Luckily spider size does not correlate proportionally with web size! Near the end of our trip we looped back down towards the Picnic Point entrance to look at the flowers in the rain garden and along the sumac boundary of the grass lawn at the base of Picnic Point. There we encountered a number of crab spiders! Crab spiders lie in wait on flowers to ambush unsuspecting insects. Their body shape is roughly reminiscent of a crab, which gives them their name.

On our way back out we had one more chance to observe the Agelenid funnel-weaver spiders in the gate fence before we dispersed. 

Many thanks to our leader Ben Klementz for this wonderful trip! Report and photos by Will Vuyk.