TARANTULA HAWKS

Pepsis sp. Coronado National Forest, Arizona. 30 Aug 2015. Netta Smith photo

     Tarantula Hawk, what a crazy name for a wasp! Well, I want to tell you all about how this fascinating insect got its name. The several hundred species of Tarantula Hawks (most in the genus Pepsis) have a global distribution at lower latitudes and are common in the Southwestern United States. First of all, the wasp strikes an intimidating figure, to say the least. Most species are metallic blue-black, with orange or black wings. They are up to 5 cm long and have a stinger up to 7 mm long in the largest species. This stinger packs such a punch that the Tarantula Hawk has the second most painful sting of any insect (it is second only to the tropical Bullet Ant). One researcher described it as " . . . immediate, excruciating, unrelenting pain that simply shuts down one's ability to do anything, except scream. Mental discipline simply does not work in these situations."

                                            

Pepsis sp. with spider. Big Bend National Park, Texas. 11 Nov 2007. Netta Smith photo

The wasp gets its name from how it raises its offspring through an effective form of parasitism. When a female Tarantula Hawk is ready to lay an egg, it flies out in search of a tarantula or other large spider. When one is located the wasp stings it, paralyzing it so it cannot move (unfortunately for the spider, things don’t get much better from here). The wasp drags the spider back into a specially prepared burrow and lays a single egg on the spider’s abdomen, then covers up the burrow entrance. When the egg hatches, the larva burrows into the spider and consumes it from the inside out, making sure to leave vital organs untouched for as long as possible to keep its host alive. The larva pupates and develops into an adult, and then when the adult emerges from the pupa, it bursts out of the spider’s abdomen and flies off to continue this fascinating life cycle of parasitism.

                                          

Pepsis sp. with tarantula. Iguazú, Argentina. Nov 1995. Dennis Paulson photo

 

Fun Fact: these wasps are actually nectarivorous, meaning that they feed on flowers and fruits and only hunt in order to find tarantulas to parasitize.

 

Sean Grealish

VENOMOUS SNAKES OF THE NORTHWEST

The Pacific Northwest has just one venomous snake, the Pacific Rattlesnake Crotalus oreganus. Formerly considered conspecific with the Prairie Rattlesnake Crotalus viridis, ours has been split from that species. The Prairie does occur just to the east in parts of Idaho and Montana.

Rattlesnakes aren't found in the wetter regions west of the Cascades summits but are common on the east side, usually in drier habitats below 3000 feet in elevation. They prefer rocky areas, probably because they can retreat into winter dens where there are a lot of crevices, but they also occur away from rocks. They are diurnal in spring when night temperatures are low but nocturnal in summer when daytime temperatures become too high for these ectothermic reptiles.

Our rattlesnakes grow to about three feet in length, but most I have seen are around two feet. I would be shocked to see one much bigger than that in Washington/Oregon. They eat primarily warm-blooded prey, especially small mammals, but they'll take a bird if they can get it, not to mention other reptiles and amphibians. The young ones especially are likely to have a broader diet of smaller animals, even insects. Rattlesnakes are pit vipers, with a pair of heat-sensitive pits just behind the nostrils that can detect a mammal's body heat in the dark. They strike their prey with a pair of fangs that fold out when used, injecting them with a potent venom. The venom is full of proteolytic enzymes and quickly causes tissue destruction and death in a small animal. The prey may have run away, the snake follows the scent trail to find the dead animal.

The venom is also a very effective defense, and any large animal would suffer even from a nonlethal bite. Over evolutionary time, natural selection favored snakes that failed to shed the very tip of their tail but instead added another segment that made noise when vibrated against its neighbors, much enhancing the tail vibration that some other snakes also practice in defense. Snakes shed their skin 2-3 times a year, so a rattle would be a fairly good indicator of the age of the snake except that terminal segments often break off.

Fortunately for Northwesterners, Pacific Rattlesnakes are not especially aggressive, and their venom is less toxic than that of their relatives to the south. Nevertheless, don't try it! Watch where you walk when in rattlesnake country, especially among rocks, and don't put your hand somewhere that you don't scrutinize first for the presence of one of these cryptic snakes.

Dennis Paulson

GREEDY GREBES GRABBING GRUB

I have been following the Pied-billed Grebes at Magnuson Park in Seattle for about two months now, and they never fail to be interesting and always offer good photo ops. Various members of the family often rest among the lily pads; presumably they are expending most of their energy digesting a good meal.

The adults continue to feed their young Oriental weatherfish (Misgurnus anguillicaudatus), a loach from Asia that has invaded the pond from Lake Washington, where it was unintentionally introduced. We have now found four species of fish in the pond, including Prickly Sculpin (Cottus asper), Pumpkinseed (Lepomis gibbosus) and Largemouth Bass (Micropterus salmoides). The first is a native species, the other two introduced long ago throughout the region for sport fishing. I still don't have any idea how they got into the pond.

Anyway, there must be a lot more loaches, or they are easier to capture, as again and again that's what I see the adult grebe feeding to the young. In this case, one young got the fish and another followed it around and around for a while. It was obvious the lucky young was trying to swallow it but was having a hard time because it couldn't slow down. But finally it managed to gulp it down.

The adults feed to the young anything than can catch, here a dragonfly, an adult male Common Green Darner (Anax junius) that perhaps was captured when it was mated with an egg-laying female at the water surface. I doubt if a grebe could pluck one out of the air.

Another one is about to swallow the larva of a California Spreadwing (Archilestes californicus), a large damselfly that is common in the pond.

There are no more ducklings for the male grebe to savage, and it seems to be getting along with the single American Coot that now lives in the pond. Maybe this is the stage in nesting when that fierce aggression is relaxed. But I've seen the male chase its own young violently on several occasions in exactly the same way, rushing it from underwater, not sure what that is all about. I still haven't been able to get a photo of it, as it happens very quickly and only once. Maybe it's just "I've had enough of all that begging."

Grebes swim amazingly rapidly underwater, and here you can see the size of the foot that, together with its mate on the other side, propels them like that. The long toes are lobed rather than webbed as they are in a duck, and both adaptations seem to work equally well.

Dennis Paulson

THE ANGELIC AND DEVILISH PIED-BILLED GREBE

Pied-billed Grebes, Podilymbus podiceps, breed at several lakes within the city of Seattle and doubtless within many other cities in the Pacific Northwest. One of our breeding sites is Magnuson Park, where one or two pairs of grebes began to breed just last year at the Shore Lagoon, the pond closest to Lake Washington. The male started calling early this spring.

And in mid May I saw the adults taking care of 5 downy young. They are very striking, with their striped heads and reddish markings. The young grebes have a strong predilection for riding on the back of the female, and I saw this numerous times. Four young at once would try to crowd onto her back, a logistical impossibility, but I saw her holding three on a few occasions. As they got larger, of course, this behavior became less likely. But it was very cute to see, a picture of parental care in a bird that can't be beat.

For several years this pond, the result of a wetland mitigation, had no fish in it. Last year the grebes fed their young primarily large dragonfly larvae, and these common insects were apparently sufficient food for the family. By this summer, Oriental weatherfish, Misgurnus anguillicaudatus, an introduced member of the loach family, had found their way into the pond somehow, perhaps through a drain into Lake Washington. So they have been the hot items on the diet this summer.

The young laze around until an adult comes up with a fish, then immediately crowd in. At first the loaches were too large, and I saw the female attempt to offer them to one young after another with no success. They swallow their food whole, so this wasn't doing it, and I assume there must have been smaller food items fed to the young when I wasn't watching. There were originally five young, but two weeks later I could see only four, so a predator may have taken one. A young bird that fledges may have moved from one narrow escape to another.

However, these grebes, especially the male, dominated the pond. He would call often and loud, sounding like a challenge to me. One day I saw something I wish I had been able to photograph. Two Mallard ducklings were following their mother across the pond, when one of them disappeared. I wondered if someone had introduced a large bass or snapping turtle into the pond, when a few seconds later the male grebe surfaced right at that spot. I didn't see the duckling again, and 10 minutes later I found it floating dead on the surface, with wounds on its head.

In additional visits, I saw the grebe chase both ducklings and adults ducks numerous times, and one of my friends saw the grebe kill two ducklings in a row. The literature about Pied-billed Grebes makes it clear that they are fiercely territorial against each other and other water birds, and a case of a Pied-billed killing the chicks of a Least Grebe was reported. The male that I watched regularly was astonishingly aggressive, chasing every bird that it came near, and I started calling it the Devil Grebe. Of course it was just exercising normal behavior for the species, and it's not the only water bird that has been reported to kill the chicks of other species. Nature is something else.

Dennis Paulson