Sun scorpion killed by black widow spider; dan.johnson@uleth.ca

A 'LOST WORLD' BATTLE: sun scorpion caught in the web of a black widow spider

(all photos by Dan Johnson, 2004)

The region near Lost River, Alberta, Canada, is a semi-arid grassland that allows survival of various arachnids, including sun scorpions and the northern scorpion. Black widow spiders (Latrodectus hesperus is the main species in the west, including Alberta) are commonly found in small mammal burrows, and between pieces of eroded sandstone and shale.
While hiking near Lost River, I found a web of a black widow spider at the top of this hill. Here are some photos that tell the story of a battle.

The female black widow spiders tends two egg sacs in a rock fissure at the top of the peak.

Black widow spider webs are typically messy, and may at first appear abandoned.

The female spider reacts to the threat of a visitor by aggressive movement, and holding web threads with each foot in order to detect movement.

In the background, a recently killed prey item is visible: a sun scorpion, genus Eremobates.

The dead sun scorpion hangs in the web next to the black widow spider egg sacs.
Sun scorpions are also called wind scorpions, camel spiders, solifugids, solfugids, or solpugids; these are members of the Order Solifugae, Family Eremobatidae.
Was this prey item cached so as to be near the egg sacs when the spiderlings hatched, or was the cadaver merely retained near the egg sacs while the adult spider fed? It must have been a battle, but the longer legs, web and powerful venom of the black widow spider meant that the sun scorpion never had a chance, once it was out in the open.

The sun scorpion appeared to have been dead less than a day, because the eyes and tarsi were dried, but the pedipalps, chelicerae and main body were not.
The pedipalps look like long legs held in front of the body, and the chelicerae are the large "fangs" that in sun scorpions are used like hypodermic needles to suck body fluid from grasshoppers, crickets, flies and other prey. The black widow spider is at level four in the food chain.

The black widow spider eggs hatched two days later. Hundreds of immature black widow spiderlings emerged in minutes. An exit hole is visible at left.

Only a few minutes after emerging from the egg sac, an immature spiderling climbs up to begin a web.

The immature attaches silk lines on a dry leaf of grass, and proceeds to build a web.

Only about one hour old, the immature black widows form a communal web.

After two hours or more, the web is a dense mat of fine criss-crossed threads. Spiderlings hang in the mesh and wait for prey.

Only a few hours old, the immature black widow spider resembles a small, translucent version of a grown spider (lateral view).

The hourglass develops closer to maturity, and does not appear on the immature (at left: several hours old, ventral view). The spinnerets are visible near the end of the abdomen.
Spider silk is made from protein, and yet it is much stronger than steel. A steel wire this small (about 30 time narrower than a hair) would easily snap.

The mother hangs in her web over her most recent prey item (a fifth-instar two-striped grasshopper, Melanoplus bivitattus).

First blood sequence.
A trapped fly is detected by web vibration and then touched tentatively by a newly emerged spiderling. Other legs are brought up to touch the prey's wing. The prey is already trapped in the messy communal web that the spiderlings made immediately after emerging.

The fly is investigated more aggressively.

The spiderling (less than a day old) moves in for the kill.

The spiderling feels for the head end of the prey. It is also "smelling", using sensory organs on the tips of the front legs.

The vulnerable body of the prey is located, and a bite is delivered. The immature spider moves away and waits for several minutes before returning to feed.
Immature black widow spiders this young appear to have venom, judging from the paralysis that quickly sets in on insects that are attacked.

The other black widow spider siblings approach for a communal feeding on the paralyzed fly.

Other spiderlings attack a struggling leafhopper, which is paralyzed within seconds.

The trademark hourglass and the prominent spinnerets (lower left) of an adult female black widow spider (western black widow, Latrodectus hesperus).
There may also be spots on the back, as you can see here.
(Medical notes on venom from emedicine)

Some black widow spiders of the same species and in the same region have an red-orange hourglass. (The one at left is eating a fly, which is out of focus because it is closer than the spider's abdomen.)
Collected at:

A female western black widow (Latrodectus hesperus) in the web.
Black widow spiders are in the family of "comb-footed spiders", the Theridiidae. They are known for having messy-looking webs, unlike the orb spiders.
I collected this one from the Willow Creek area near Fort Macleod, Alberta.

The black widow shown at the left was given to me by M. Mori, who collected it in Kelowna, B.C. This one has a broken hourglass. It appears to be the northern black widow, L. variolus.

The spinnerets are at the tip of the abdomen (posterior to the hourglass), and are essentially spigot-like taps that produce silk.

(Black widow species: mainly Latrodectus hesperus in the west, including Alberta, and L. mactans and L. variolus are usually found in the east, southeast and midwest.)

The slit anterior to the hourglass (shown at left) is the female sex organ, the epigyne. The sex organs of the male are palps that hang in the front, like boxing gloves.
Unlike most insects, which have sex organs at their posterior ends, spiders have their sex organs in the middle of the underside (female) or at region of the mouthparts (male). During copulation, they rear up and appear to be preparing to dance.

Some other grassland arachnids that you might see:
The arachnids include the scorpions, false scorpions, sun scorpions, mites, ticks, and daddy-long-legs.

Geolycosa missouriensis is a large wolf spider that lives vertical tunnels 10 to 30 cm in sandy grassland soils. Dunes and blowouts are good places to find them. I find them mainly in years that are not extremely wet or extremely dry, (for example, late summer of 1994, 1995 and 2004), but they are always rare in the northern great plains, especially in Canada.

A Missouri wolf spider (Geolycosa missouriensis) investigates the edge of my hand, feeling the air and my skin for a way down.

The Missouri wolf spider can be dark grey or rusty tan and grey. They are large but not poisonous to people.
The eight legs are long, and the two smaller appendages that look like legs are the pedipalps.

The eight eyes of the Missouri wolf spider give a wide field of detection forward and above.
The eyes sit on the carapace. The body is called the cephalothorax. The two large rusty objects that appear hairy are the chelicerae. At the bottom they each hold a fang.

Cat-faced spiders (Family Araneidae, the Orb web spiders) tend to locate their webs under dead wood, overhangs or guarded locations such as animal burrows. This is why they are often called barn spiders. I found this large female Araneus on an old building at a prairie farm in Saskatchewan (Sept, 2004).

Here is another view of the "cat's face".

Banded garden spiders (Argiope trifasciata) were rare on the northern grassland before 1999, and in 1999 increased in numbers. They seem to thrive in dry weather. The peak year in Alberta and Saskatchewan was 2000, when at some grassland sites the majority of depressions and mammal burrows contained a successful banded garden spider web. At the same time, black widow spiders, previously common on southern Alberta grassland, became rarer, and difficult to find in searches of burrows and dead wood.
Banded garden spiders declined from this peak in 2000, followed by moderate increases in 2002-2003. In 2004, banded garden spiders were less common, but still above 1983-1998 levels.
The large female at the left waits in an orb placed over a ground squirrel burrow, but what it will catch will be grasshoppers.

As with other spiders, the male is much smaller. Up to three males can often be seen hanging in the web of a female.
These are from my riparian (streambank area) research sites near Barnwell, Alberta.

The Northern scorpion, Paruroctonus boreus, is found northern grasslands and semi-desert areas. This is Canada's only species of true scorpion. It is found in British Columbia, Alberta (widest disribution) and Saskatchewan.