Woodlouse Hunter

This installment of “Spider Sunday” features yet another arachnid that causes undo consternation and fear among homeowners who encounter it inside their residences. The Woodlouse Hunter, Dysdera crocata, North America’s only representative of the family Dysderidae, is not dangerously venomous to the average, healthy human being or family pet.

That is not to say that this species doesn’t look formidable. It ranges from 9-15 millimeters in body length, and has very large chelicerae (jaws) with long fangs. The cephalothorax and legs are bright reddish brown or orange, and the abdomen beige or gray in color. These spiders have only six eyes instead of the usual eight that most spiders have, and they are arranged in a compact semi-circle at the front of the cephalothorax.

The Woodlouse Hunter is actually native to the western Europe, but has been introduced over much of the globe through commerce and other forms of human travel and enterprise. Here in North America it is most common in urban areas, favoring disturbed habitats in both forest and field.

Dysdera crocata is nocturnal, hiding by day under stones, logs, and boards or other debris. It ventures out at night in search of prey. The preferred prey is apparently terrestrial isopods known as woodlice, also called “sowbugs.” Sowbugs are also native to Europe, but now abundant in the U.S. and Canada. The spider uses its enlarged jaws and long fangs to pierce their armored prey, or turn it over and stab it in its soft underbelly. Captive Woodlouse Hunters will readily take other small animals as prey, so they are more plastic in their feeding habits than their name suggests.

Sowbug

The life cycle, revealed by captive rearing, is lengthy. It takes about eighteen months for an individual spider to reach maturity after hatching from the egg. A given specimen can then live an additional two to three years. Mating probably take place in the spring. Females contain a batch of up to seventy (70) ova within a rudimentary egg sac consisting of only a few strands of silk.

Look for the Woodlouse Hunter under objects outdoors. They may be hiding inside an oval, silken retreat, which they spin for purposes of molting and overwintering. Sometimes, the spiders stray indoors, and that is where they are most conspicuous. While there have been documented bites by this species, the symptoms amount to only localized pain lasting an hour or so, due mostly to the mechanical injury caused by those long fangs.

Dysdera is easily confused with Broad-faced Sac Spiders I the genus Trachelas, which have a nearly identical color pattern. Note that Trachelas has eight eyes, arranged in two rows across the wide front of the cephalothorax. Trachelas also lacks the long jaws and fangs of the Woodlouse Hunter.

Trachelas

I am keeping the specimen of Dysdera imaged here as a potential display animal I can take to public educational events. The more that can be done to alleviate our collective fear and loathing of spiders the better, and the Woodlouse Hunter can be a great ambassador for that mission.

Sources: Bradley, Richard A. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.
Jacobs, Steve. 2013. “Spider: the Woodlouse Hunter,” Fact Sheet. Penn State University Entomology Department.
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds). 2005. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

"Is it poisonous?"

Hardly a day goes by when I am not asked some version of this question. Maybe it is phrased “Is it dangerous?” or “Is it venomous?” This illustrates just how paranoid we have become of other life forms on this planet. Let’s clarify the definition of each of these terms, and the relative risks involved with each.

Most of the time, people use the terms “poisonous” and “venomous” interchangeably. What they usually want to know whether a given spider, scorpion, or insect is venomous. Venomous animals possess toxins that they deliver to a victim by biting or stinging. Nearly all spiders are venomous, as that is how they kill their prey. Only a handful of spiders are dangerously venomous to the average, healthy human being. Here in North America, the only spiders confirmed to be potentially dangerous are widows (genus Latrodectus), and brown spiders (genus Loxosceles). This is not to say that the bite from *any* spider cannot spark an allergic reaction in someone hypersensitive to venoms.

Western Black Widow (female)

What is generally exaggerated is the risk of being bitten by a spider. The likelihood of being envenomated by a spider is quite miniscule, especially if you take simple precautions like those suggested in this article at Spiders.us.

Some venomous insects can come as a surprise to the uninformed or uninitiated. Several caterpillar species, for example, have stinging spines or hairs that can cause excruciating pain, at least in some people. Be careful not to touch hairy or spiny caterpillars.

Flannel Moth caterpillar

Ironically, tarantulas in the genus Aphonopelma will kick tiny, barbed hairs off of their abdomen instead of biting in self-defense. The hairs become airborne and, if inhaled or otherwise contact mucous membranes, cause severe irritation or even allergic reactions. Some people who handle tarantulas, or even the molted exoskeleton, may pay for the experience with contact dermatitis.

Wheel Bug adult

Many species of ants other than fire ants are capable of stinging, as can “velvet ants,” wasps in which the female gender is wingless and may resemble a large, hairy, brightly-colored ant. Assassin bugs like the Wheel Bug, and aquatic bugs like giant water bugs (aka “toe-biters”), backswimmers, and water scorpions, have a venomous bite to immobilize prey, but they can bite in self-defense, too. I can speak from experience that it is not pleasant.

Giant Centipede

Centipedes, fast-moving, snake-like arthropods with “too many legs,” are venomous, their first pair of legs modified into fangs they use to subdue their prey or defend themselves. Scorpions, arachnids related to spiders have a venomous stinger at the end of their telson (“tail”), but only the “bark scorpion,” Centruroides sculpturatus, is dangerously venomous. It occurs only in Arizona, western New Mexico, southern Nevada and Utah, and extreme southeast California.

The term poisonous means that an organism is toxic if ingested (swallowed). A startling number of insect species actually are poisonous and it pays to learn which ones, especially if you have curious toddlers prone to putting things in their mouths. Fireflies are very poisonous, as their bodies contain lucibufagins, toxins closely related to the toxins in toads.

Blister Beetle, one of many species

Blister beetles (image above) are aptly-named, for when molested they ooze a liquid substance containing cantharidin, an irritant that can raise blisters on sensitive skin. Even worse, if eaten, they can be lethal. Ranchers must be careful that blister beetles are not accidentally baled in hay. Horses that swallow beetles along with hay can die.

Millipedes, slow-moving, worm-like arthropods with lots of legs, are vegetarians, but most can defend themselves with harsh chemical secretions. Some species, like the one shown below, ooze cyanide compounds to repel potential predators. Others produce substances that can stain, or even burn, the skin.

Flat-backed Millipede

Luckily, many venomous and poisonous insects and spiders are aposematic. That is, they are marked with bright, contrasting “warning colors” such as black and yellow, orange, or white. There are many completely harmless insects that mimic those dangerous species, but when in doubt it pays to avoid handling brightly-colored animals.

While I do want people to find fascination in insects, spiders, and other invertebrates, I also want the public to stay safe and healthy. Be careful out there.

The Emerald Ash Borer Invades Colorado

I am usually excited in the positive sense when insects make headlines, but there are exceptions. It was devastating to learn recently that the Emerald Ash Borer, Agrilus planipennis, has been detected here in Colorado. Why is this discovery such a big deal? It has to do in part with the customary response to this exotic invader in other locations where it has shown up.

The Colorado Department of Agriculture announced on Friday, September 27, 2013 that the Emerald Ash Borer (EAB) had been discovered in Boulder County earlier in the month. While ash trees are apparently not native to Colorado, they are planted widely as part of the “urban forest” in many cities along the Front Range. Consequently, those trees are vulnerable to this invasive pest.

The reaction of many municipalities to the presence of EAB is the pre-emptive removal of the insect’s host trees. Visions of a wholesale slaughter are going through my mind right now. It is not pretty. It is costly, too, and leaves one less alternative for greenery and shade in what is a pretty bleak landscape on the fringe of the Great Plains. Shade is hard to come by, and there are few tree species that don’t have objectionable side effects. Cottonwoods shed copious amounts of cottony seeds in the spring. Locust trees grow quickly but their falling leaves get sucked into car air filters and find their way into every crack and crevice.

The thing that is really tragic is that the spread of the EAB is pretty much preventable. Various agencies and organizations have tried to get out the message about not moving firewood between states (even between counties), but the plea has either fallen on deaf ears, or not been broadcast loud enough. This is such an important message that it really warrants the Ad Council’s help in airing public service announcements on television and radio.

What is the history of this pest, you ask. According to EmeraldAshBorer.info, the Emerald Ash Borer was first discovered in the United States near Detroit, Michigan in 2002. At least, that is when entomologists first recognized it. It could have been present prior to 2002. Authorities surmise that it probably arrived in solid wood packing material originating from its native Asia. In short order the EAB was also found in Ontario, Canada, Ohio, and northern Indiana (by 2004). More were detected in northern Illinois and Maryland in 2006, then western Pennsylvania and West Virginia in 2007, followed by Missouri and Virginia in 2008. Since then it has also turned up in Minnesota, New York, Kentucky, Iowa, Tennessee, Connecticut, Kansas, Massachusetts, New Hampshire, North Carolina, Georgia, and now Colorado.

The life cycle of the beetle makes it difficult to quickly detect and almost impossible to control. The adult beetles typically emerge in mid-late May, with peak numbers in late June. Mated females begin laying eggs within two weeks of their emergence. The larvae hatch in about one to two weeks and begin boring into the inner bark and cambium layer of the host tree, disrupting the transportation of nutrients to the top of the tree. The larvae continue boring from late July to early October, overwintering in a chamber where they will pupate in the early spring. Sometimes the cycle is extended to two years.

The only symptoms of an EAB infestation outwardly visible are the gradual and subtle thinning of the tree’s canopy, and dying of branches in the uppermost reaches. Small trees can be killed by the beetle in one or two years, whereas larger trees may succumb in 3-4 years. The beetle probably selects stressed or otherwise already weakened trees as preferred hosts, but healthy trees can be attacked, too. The ongoing drought in the Front Range enhances the probability of the EAB becoming a widespread problem very quickly.

Please be on the lookout for the Emerald Ash Borer in your own state, province, or county, whether or not the species has already been detected there. Report your observations to your state department of agriculture, taking them specimens whenever possible. Thank you.

When "Arachtober" Attacks!

October is one of my favorite months, made all the sweeter in the last three years because I have participated in the “Arachtober” group on Flickr.

Many folks who photograph insects and other small animals save the spider images they have accrued over the year to share with the Arachtober pool. This is because one of the few rules of the group is that you post only those images that have not appeared on your Flickr photostream previously. It is worth the wait.

Sometimes, participants forget that there are other arachnids besides spiders: mites, ticks, scorpions, whipscorpions, pseudoscorpions, harvestmen, and others. A few members of the group actually find things like ticks to be too disgusting to embrace even in the artistic sense. A few scorpions and “daddy long-legs” pictures will still manage to appear, though.

The biggest challenge to Arachtober’s popularity this year may be the graphic changes brought to Flickr as a whole by its new owner, Yahoo!. Fewer people view my own photostream any more because of the new format that has rendered Flickr just a shadow of its former clean, aesthetic past. The initial outrage demonstrated by the Flickr faithful has either faded, been completely ignored by Yahoo!, or both. The future of photosharing may be Facebook, Pinterest, Twitter, and Instagram, but mobile devices really don’t do quality images justice.

All the same, I invite you not only to follow Arachtober daily, but to participate as well by sharing your own images of all things eight-legged. Thank you.