June 20th – No entry today, but Darwin was still awash in spiders (now there is a pleasant thought). In many cases, Darwin watched spiders as they hunted, stunned, and drained their prey. But in one case, the hunter became the hunted:
“Certain wasp-like insects, which construct in the corners of the verandahs clay cells for their larvæ, are very numerous in the neighbourhood of Rio. These cells they stuff full of half-dead spiders and caterpillars, which they seem wonderfully to know how to sting to that degree as to leave them paralysed but alive, until their eggs are hatched; and the larvæ feed on the horrid mass of powerless, half-killed victims—a sight which has been described by an enthusiastic naturalist as curious and pleasing!” (Voyage of the Beagle)
He continues with a specific story. The characters in this tale of action and adventure are what Darwin refers to as:
“Pepsis” – This is the genus name for the “tarantula hawk”. That is a pretty cool name, especially when you learn that it is not a bird but a type of wasp. They can be up to 5 cm long with a stinger up to 7 mm!
“Lycosa” – As the Greek might suggest, this is a genus of wolf spiders (family Lycosidae). Wolf spiders are proficient hunters, often ambushing their prey. They tend to have 2 larger eyes (and 6 smaller ones) which reflect the light of a flashlight, making them an eerie sight to see in your basement at night.
Lycosa erythrognatha from Brazil (from the BugNation forum):
Darwin proceeds to describe the battle of the “hawk” and the “wolf”:
“I was much interested one day by watching a deadly contest between a Pepsis and a large spider of the genus Lycosa. The wasp made a sudden dash at its prey, and then flew away: the spider was evidently wounded, for, trying to escape, it rolled down a little slope, but had still strength sufficient to crawl into a thick tuft of grass. The wasp soon returned, and seemed surprised at not immediately finding its victim. It then commenced as regular a hunt as ever hound did after fox; making short semicircular casts, and all the time rapidly vibrating its wings and antennæ. The spider, though well concealed, was soon discovered; and the wasp, evidently still afraid of its adversary’s jaws, after much manœuvring, inflicted two stings on the under side of its thorax. At last, carefully examining with its antennæ the now motionless spider, it proceeded to drag away the body. But I stopped both tyrant and prey.” (Voyage of the Beagle)
Interesting that Darwin stopped them – though I wonder, does this mean he let them both go or squashed them both?
As Darwin noted in the first quote, the fate of the spider in this story is not a good one. The tarantula hawk merely stuns the spider before dragging it back to her burrow with her grappling hook-like claws (and it is a “her” in this case). One article calls this burrow her “burial vault”, as the wasp will now lay an egg on the spider’s abdomen, and seal up the burrow. When the egg hatches, the young grub has a feast waiting – a living spider – which it proceeds to devour, keeping it alive and “fresh” for as long as possible. And to think spiders have a reputation for being macabre!
Speaking of pain…did you know that the entomologist Justin O. Schmidt devised a scale for describing the pain of hymenoptera (bees, wasps and ants) stings called the Schmidt Pain Scale? And, although they don’t often sting humans, the tarantula hawk’s sting is one of the most painful stings on that scale (second only to bullet ants)? The scale runs from 0 to 4, and if you have ever been stung by a honeybee, you’d be glad to know that it is right in the middle – a 2 on the scale. There are only three hymenoptera that warrant a 4 on the scale – the warrior wasp, the bullet ant, and our friend the tarantula hawk. (It seems obvious from the name that the person who had the honor of naming the first two, also had the honor of being stung by them.) One scientist (via DesertUSA.com) describes the pain of a tarantula hawk sting as, “an electric wand that hits you, inducing an immediate, excruciating pain that simply shuts down one’s ability to do anything, except, perhaps, scream”.
Read more about the Schmidt Pain Scale in an entertaining article on The Straight Dope. Oh, and watch our for bullet ants! (RJV)