Desert Demon, the Solifuge

You can often tell what opinion the human race has of another animal by the number of aliases we assign to it. Just like the law-abiding citizens of the Old West, we tend to give nicknames to creatures we consider unsavory or downright mean. Such is the case with the arachnids of the order Solifugae. Depending on your geographic location, you may be familiar with them as “camel spiders,” “sun spiders,” “wind scorpions,” or “solpugids.” Not that their reputation is entirely undeserved, but these are fascinating and enigmatic invertebrates.

Two things are immediately apparent about a solifuge that are cause for alarm. The first is the animal’s sheer speed. They don’t get the name “wind-scorpion” for nothing, as they do “run like the wind,” and on only six of their eight legs. They are more agile than an NFL halfback, too. Attempts to capture them can leave you face down in the sand while at the same instant the solifuge is crossing the county line. I recall chasing a small one around the floor of an outdoor dining hall at a camp in eastern Oregon to the point of dizziness (me; the solifuge was fine).

The second thing about a solifuge you notice is the size of its jaws. Known to scientists as “chelicerae,” this pair of mouthparts can take up nearly one-third the body length of some species. They easily have the largest jaws for their size of any terrestrial animal (invertebrate at least). Each chelicera consists of a fixed upper portion and an articulated bottom joint combining to form the equivalent of a nutcracker or pair of pliers. Armed with teeth and filled with muscle, they are formidable weapons. These are non-venomous animals, but they do so much mechanical damage to their prey so quickly that they don’t need venom.

There are roughly one thousand species of Solifugae known globally, in 140 genera, and twelve families. Only two families (Eremobatidae and Ammotrechidae) occur in North America. There are about 100 species in the southwest U.S., half the North American total. The order reaches its zenith of diversity in the Middle East.

The source of much recent misinformation about “camel spiders” has come chiefly from United States servicemen and women stationed in the Persian Gulf, during both the first Gulf War in 1991 and the present conflict. Camel spiders are abundant, conspicuous arthropods there, but contrary to popular reports the animals do not reach the size of dinner plates (North American solpugids rarely exceed one inch in body length), they don’t literally run screaming across the dunes at 25 mph (they make no noise, and can only sprint at about 53 cm/second for short bursts), and they certainly don’t eat the stomachs of camels or the faces of sleeping soldiers. A widely-circulated image of a pair of camel spiders and a thorough de-bunking of the commentary that accompanies it can be found at Snopes.com.

Reality is usually far more interesting when it comes to arthropods, and camel spiders are no exception. They are highly adapted to the arid environments they thrive in. They are covered in fine hairs that help insulate them from the desert heat, with sparse, longer setae that act as sensors which help find prey by touch. There are also rows of sensory organs on the underside of the hind legs. These stubby, hammer-shaped appendages are called “racket organs” or “malleoli.” They are basically chemoreceptors, literally sniffing out information about the substrate the animal is traversing. Solpugids can even detect subterranean prey at a shallow depth, through the malleoli and tapping movements of the pedipalps.

The pedipalps, which in solpugids are easily mistaken for the first pair of legs, are long, stout, and tipped with “suctorial” organs that are useful to the animal when it needs to ascend vertical surfaces, or pin down struggling prey.

The first pair of legs, immediately behind the pedipalps, are very slender, and also used as sensors, waving constantly along with the pedipalps. A cornered camel spider may rear up, waving both pairs of appendages menacingly, and opening its jaws.

Given their overall aggressive nature, one wonders how camel spiders are able to reproduce without killing each other first. Indeed, the “attack phase” during courtship can easily be mistaken for an attempt at cannibalism by a male intent on mating. The female repels his advances, flees, or assumes a submissive posture. The male then grasps her mid-body and massages her with his jaws while stroking her with his pedipalps and first pair of legs. He may lift and carry her a short distance, or simply continue courting at the initial spot of contact. He eventually secretes a droplet of sperm from his genital opening, cradles it in his jaws, and uses his chelicerae to force the sperm into the female’s genital opening. Mating rituals vary among the different families of camel spiders, but the basics are consistent.

Look for camel spiders mostly at night. Some are active by day (hence “sun spider” as an alternative name), but most North American species are nocturnal. They can be seen around outdoor lights where they prey greedily on insects that have fallen to the ground. By day, flip over boards, flat stones, and cow patties, as solpugids often seek refuge under such debris. Be sure to return the object to its original position to afford shelter to other organisms. Some species actively excavate burrows where they weather the daytime heat.

Search for virtual solpugids online at informative websites like The Arachnid Order Solifugae, and Solpugid Productions. The Biology of Camel-Spiders, by Fred Punzo (Kluwer Academic Publishers, 1998) is the best book reference to date.

Given their frenetic lifestyle, solpugids are not recommended as pets. They need their entire adult lifespan to find mates and reproduce. Enjoy them where you find them; and be glad you aren’t a prey-size animal yourself.

Wasp Wednesday: Blue Mud Dauber

Among insect architects, the Blue Mud Dauber, Chalybion californicum, is not Frank Lloyd Wright. What it does have going for it is a remodeling career. Oh, and a reputation as a fierce enemy of black widow spiders.

Blue mud daubers are solitary wasps in the family Sphecidae. Females take over abandoned nests of their cousin, the Black and Yellow Mud Dauber, Sceliphron caementarium. While Sceliphron gathers mud to make her nest, Chalybion carries water to an old nest to soften it and remold it to her needs. The result is a very lumpy version of the normally smooth Sceliphron nest.

Chalybion makes up for any engineering deficiencies with a persistent, clever, and energetic approach to catching prey. The female wasp is able to land on a spider web without getting entangled, then do a convincing impression of an insect that is in distress. She plucks the web and draws the spider out. The poor arachnid comes dashing down a thread expecting dinner and instead seals its own doom. The blue mud dauber stings the spider into paralysis and flies it off to her nest.

Among the known spider hosts for the blue mud dauber are black widows, specifically the Southern Black Widow, Latrodectus mactans. For a highly entertaining account of this I recommend chapter five (“The Terrible Falcons of the Grassland”) in Hunting Big Game in the City Parks, by Howard G. Smith (New York: Abington Press, 1969). Additional spider hosts include mostly other cobweb weavers, family Theridiidae, small orb weavers (Araneidae), and the odd lynx spider (Oxyopidae), crab spider (Thomisidae), or jumping spider (Salticidae).

Mud daubers in general stuff a multitude of spider victims into each mud cell before finally sealing it with a curtain of mud. A single egg had been laid on the very first spider stored at the bottom of the cell. The wasp larva that hatches then gradually consumes all the spiders, leaving a smattering of legs as the only indication there was ever anything else in there with them. The mature larva then spins a papery silken cocoon inside which it pupates. A few weeks later (or come spring if it was overwintering) an adult wasp chews a round hole in the end of the cell and exits. Holes in any other part of the mud nest indicate that some kind of wasp parasite chewed its way to freedom instead of the mud dauber.

Male mud daubers are far less industrious than their female counterparts. Their sole mission is to father the next generation. Meanwhile, they are content to sip nectar from flowers or extrafloral nectarines. They also like oozing sap from wounded trees and, perhaps most of all, the “honeydew” secreted by aphids and scale insects. Both genders of mud daubers like this delicacy, which is nothing more than the sugary liquid waste produced by those sap-sucking buggers.

Meanwhile, after a heavy day of drinking, males may gather in “bachelor parties” to sleep it off during the night. These congregations of normally solitary wasps can cause a bit of anxiety in people who confront them. Take a look at this image and comment thread for an example.

It should be noted that there are actually two species of Chalybion found north of Mexico. C. californicum is transcontinental in the U.S. and southern Canada, while C. zimmermanni ranges from Tennessee and North Carolina south to Florida and west to Texas, Arizona, and into Utah. I am curious as to whether the males I photographed recently in southern Arizona are C. zimmermanni given the smoky, rather than violaceous, wing coloration (see below).

Enjoy making your own observations of these wasps. They are not the least bit aggressive and, because they often nest on the exterior of buildings, are easy to watch.

Sources:
Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley: Universithy of California Press. 695 pp.
Krombein, Karl V. et al. 1979. Catalog of Hymenoptera in America North of Mexico. Washington, DC: Smithsonian Institution Press. Vol. 2, pp 1199-2209.

Wasp Wednesday: Steniolia elegans

Sand wasps have to be among the most industrious of all insects. I was reminded of that back on June 18 when I encountered a female of Steniolia elegans digging a burrow in the middle of the Oracle Ridge Trail on Mount Lemmon in the Santa Catalina Mountains just north of Tucson, Arizona.

This ornately-marked insect is a member of the family Crabronidae (older references have them placed in the family Sphecidae), a group of solitary wasps. There are collectively fourteen species in the genus Steniolia in North America, all of them western in their geographical distribution. Four occur only as far north as Mexico. There is a lot to like about them. They hunt flies for one thing. The female exhibits parental care, too.

While each female digs her own burrow, usually in dry, powdery soil rather than sand, many females may nest in close proximity to one another. The burrow terminates in a single cell at a depth of 7-17 centimeters underground. The female covers the burrow entrance while she is away hunting prey. She uses subtle landmarks to help her find it again upon her return. Meanwhile, we can’t remember where we parked the car.

Steniolia elegans hunts mostly bee flies (family Bombyliidae) and flower flies (family Syrphidae) as food for her single larval offspring. Once she subdues a fly, stinging it into paralysis or even killing it outright, she takes the victim into her burrow and lays an egg on it. The larva that hatches then begins eating the fly. The female wasp goes hunting again, bringing flies to the developing grub throughout its life. This is called “progressive provisioning,” much like what birds do in feeding their nestlings.

Once the larval wasp ceases to feed its mother closes the nest burrow a final time and departs to begin another nest. The grub then pupates, emerging as an adult wasp weeks later (or months if it is overwintering).

Members of the genus Steniolia also engage in a strange nightly ritual. Both genders can come together to form dense, spherical sleeping clusters. Mating apparently takes place at these “slumber parties,” which disperse again at daybreak.

These wasps are not without their enemies. Satellite flies, mentioned in last week’s installment of Wasp Wednesday, plague these wasps, too. Velvet ants (which are actually wingless female wasps) will dig open the burrow of a sand wasp and lay an egg of their own in the burrow. The larval velvet ant then consumes the larva of the host wasp, after the host has finished feeding itself. A cuckoo wasp, Parnopes edwardsii, behaves similarly as a parasite.

Look for male Steniolia at flowers like thistles where their long, tongue-like mouthparts can reach nectar buried deep. Females visit flowers also, but are mostly busy nesting and hunting. Steniolia elegans ranges widely in the west, from southeast Washington state, Idaho and Wyoming south through much of Mexico.

Alas, this particular specimen I imaged eventually gave up on digging her burrow. It might have been for the best as the trail gets a lot of recreational human traffic.

News Flash

I will be starting a new, part-time job shortly at the Tucson Botanical Gardens. My title will be "Assistant Butterfly Curator" for the Butterfly Magic exhibit of live butterflies that runs from October through April. Elizabeth Willott, Curator of Butterflies, will be my supervisor there. I am very much looking forward to learning how to better train and manage volunteers, which will account for most of my duties.

I am still actively seeking full-time work online, in media, and museums, but am very grateful to TBG for extending me this offer. I will still have time to continue freelance work as well.