Ask The Entomologist

Harvestmen, or Daddy-Long-Legs

Earlier this week, I met a Harvestman while making supper. It had stowed away on some kale from the garden, and was still walking about on it… even after a week or so in the refrigerator.

The refrigerated Harvestman was promptly photographed and released in our garden’s cold frames.

Harvestmen have a rather well-known urban legend. Perhaps you’ve heard people say that “they’re the most venomous spiders in the world, but are harmless to humans because their fangs are too small to puncture our skin.”This myth is mostly untrue. While Harvestmen are harmless to humans, they are NOT spiders – they’re closer kin to scorpions and mites. Additionally, they don’t have venom, though they do have some chemical weapons and chemical defenses. Some species, however, rely more on physical armor than chemicals.

This Ecuadorian Harvestman sees no reason to limit itself:
it has spiny armor and is putting chemicals on an arm, which it will then use as a whip!

While many people call Harvestmen “Daddy-Long-Legs”, this common name is rather vague, and I try not to use it. It can also refer to Crane Flies and Cellar Spiders, and I prefer being specific. Incidentally, the harvestmen myth is equally untrue for those two organisms as well.

Unlike most other arachnids, Harvestmen aren’t primarily hunters. Actually, many Harvestmen prefer to eat things that are already dead… They’re great scavengers, happy to eat dead vertebrates, dead invertebrates, and even droppings. One European species has been claimed to hang about bee hives, eating the dead worker bees that worker bees on the custodial shift are tossing out.

Harvestmen are beneficial for our gardens though, because they can and do hunt small insect pests such as springtails. They use their tiny little pinchers and fancy chemical glue to catch their prey. If you’d like to see their feeding behavior yourself, I’d suggest waiting by a porchlight at night – I’ve found that they like to ambush and eat little moths. If you’re a bit more hands-on, Harvestmen are easy to keep in captivity, and could make a great science project (drop me an email if interested in more details).

As for why my Harvestmen was still alive in the refrigerator, these invertebrates tend to be Cold-Tolerant and Freeze-Avoidant. They’d prefer to be warm, increasing their odds of survival, so in autumn one can find large aggregations of Harvestmen. Sharing warmth, sheltering from the elements, and trying to survive the winter. This overwintering behavior frequently happens in caves, though in eastern North America, Harvestmen also overwinter in leaf litter.

A disturbed aggregation of overwintering Harvestmen from a cave in Northern Tennessee.

What have you observed Harvestmen doing?
Hunting? Mating? Overwintering?

Ask The Entomologist

Ichneumonid wasps, imposing allies

Last Thursday I saw this lovely Ichneumonid wasp (pronounced ICK-new-mon-id, from Greek “Ιχνευμων” which means “Tracker”). Most of the time I see Ichneumonids, they’re on the sides of trees, ovipositing (laying eggs) in boring insect larvae. This one’s behavior was very odd indeed.

An Ichneumonid wasp, Pimpla pedalis, oviposits into a newly split piece of Douglas Fir.

As you can see, this particular Ichneumonid wasp was laying her eggs inside a freshly split piece of Douglas Fir … or rather, inside a boring insect inside the Douglas Fir. Curious to see what insect she was laying her eggs inside, I peeled away layer after thin layer of wood …

Uncovering the beetle grub (at left, mid-height) the wasp laid her eggs in.

… And after an inch and a half of wood was removed, exposed a boring beetle grub. This is a Jewel Beetle grub, a member of family Buprestidae. These beetles can be lumber pests, though they’re unlikely to damage treated wood. While none of our Montanan Jewel Beetles are quite as bad, the Emerald Ash Borer has been devastating to ash trees throughout eastern North America.

There it is, a Buprestid beetle grub, just to the left of the burrow it gnawed in the wood.

I have very fond childhood memories of Giant Ichneumonid wasps. Most Sundays, my family would go to the arboretum of South Dakota State University’s then-public gardens. Among my favorite things there were some large multi-trunked cedars, which, in autumn, attracted some very large wasps. Presumably, the cedars also had very large wood-boring larvae that the Ichneumonids were parasitizing. Despite being a typical small human, making noise, climbing trees, and being generally bothersome, the Ichneumonid wasps never showed any sign of interest in me.

While their large stingers and stinger sheaths look quite formidable, Ichneumonid wasps very rarely sting mammals or other large animals. Unlike typical colony-living wasps and bees, Ichneumonid stingers are almost exclusively used for laying eggs inside of host insects. Eventually the eggs hatch, and the baby wasps eat the host insect from the inside out. Parasites that always kill their hosts are called parasitoids (think of the Xenomorphs from the Alien movies).

Fortunately for us, in addition to not stinging us or our pets, Ichneumonid wasps are also great at controlling garden pests. They take out a variety of garden pests (tomato hornworms, cabbage worms, etc.) as well as lumber pests (long-horned beetles, jewel beetles, bark beetles, etc.).

All in all, they’re neighbors I’m quite glad to have.