Wasp Wednesday: Elm Sawfly

Finally! I have been looking for an adult Elm Sawfly, Cimbex americana, for decades, ever since seeing pinned specimens in college back in the early 1980s. My quest ended this past Monday, June 25, when I happened upon a huge male specimen in the middle of a meadow in Emerald Valley, Colorado.

The Elm Sawfly is a large, robust insect about 20-25 millimeters in body length. They appear even bigger, especially the males with their beefy “thighs” (femora) on the middle and hind legs. The jaws of both genders are strong, and used to strip bark from twigs, sometimes girdling them in their efforts to reach the tasty sap. The clubbed, relatively short antennae are a characteristic of all members of the family Cimbicidae. The overall plump appearance often convinces people that these insects are bees rather than wasps.

The larvae of these wasps feed not on pollen, nectar, or other insects paralyzed and provided by their mothers. Instead, sawfly larvae feed on plant foliage. Despite the name “Elm Sawfly,” Cimbex americana feeds on other trees as well, especially willow, but occasionally on basswood (linden), birch, poplar, alder, and maple. At maturity, the caterpillar-like larva can be two inches (43 millimeters or so) long.

How do you tell a sawfly larva from the caterpillar of a butterfly or moth? True caterpillars have no more than five (5) pairs of prolegs, the “false legs” along the length of the abdomen that look like suction cups. Sawfly larvae have seven (7) pairs of prolegs.

When they are disturbed, Elm Sawfly larvae coil themselves and prepare to release volatile chemicals from glands in the thorax if necessary for their self-defense. They also rest in a coiled position. The rough, pebbly texture, and black midline dorsal stripe help to identify these greenish, yellowish, or whitish larvae. Look for them mostly between June and October, but note that I found the specimen pictured here on May 7 in South Carolina.

The mature larvae crawl to the ground and spin a tough, papery cocoon around themselves amid leaf litter or just below the surface of the soil. There they remain as larvae through the winter, pupating the following spring. There is only one generation per year.

The adults are sexually dimorphic in color. Shown here is a male. Females have the abdomen black with yellow horizontal bands interrupted in the middle. There is some variation in color and pattern from one geographic area to another. This is a very widespread insect, found in the U.S. and Canada from the Atlantic seaboard to the Rocky Mountains, and also the Pacific coast states north to Alaska.

Females of the Elm Sawfly use a saw-like ovipositor to insert eggs in the leaves of the host tree. They do not have a stinger. Both genders simply look intimidating. Males may defend territories. The one I found on Monday I startled from its perch, but after a wide orbit it flew right back to that one shrub, elevated only a little above surrounding vegetation.

The Elm Sawfly does have its enemies, including an egg parasite, Trichogramma minutum, a very tiny type of wasp. A large ichneumon wasp, Opheltes glaucopterus barberi, is an internal parasite of the sawfly larva. The sarcophagid fly Boettcheria cimbicis has been reared from the pupal cocoons of the Elm Sawfly.

See if you can find this species in your own region. Do you find it to be common? Do populations vary from year to year? While this species is rarely a pest (it has been known to defoliate shade elm trees, especially in the northern Midwest), it would pay to know more about it.

Sources: Drooz, Arnold (editor). 1985. Insects of Eastern Forests. Washington, DC: U.S. Department of Agriculture, Miscellaneous Publication No. 1426. 608 pp.
Essig, E. O. 1958. Insects and Mites of Western North America. New York: The Macmillan Company. 1050 pp.
Furniss, R. L. and V. M. Carolin. 1977. Western Forest Insects. Washington, DC: U.S. Department of Agriculture, Miscellaneous Publication No. 1339. 654 pp.
Stein, John D. 1974. Elm Sawfly. Forest Pest Leaflet 142. Washinton, DC: U.S. Forest Service, U.S. Department of Agriculture.

Spider Sunday: Beach Wolf Spider

Life is literally a beach for the Beach Wolf Spider, Arctosa littoralis. This member of the family Lycosidae ranges throughout the United States and southern Canada, so obviously not all individuals live by the seaside. However, this spider is partial to sandy habitats such as dunes, stream banks, and blowouts.

The specimen shown here is one I encountered in Massachusetts on Cape Cod National Seashore under cover of darkness on July 25, 2009. It had killed what was probably an already weak worker honeybee. This worked to my advantage because the arachnid was not racing across the sand, outrunning me, my light source, and camera.

Arctosa littoralis is a fair-sized spider, mature males and females measuring 11-15 millimeters in body length. Their sprawling legspan adds to their perceived size. Still, good luck spotting one if it isn’t moving. The camouflage of this species is amazingly effective. Mottled gray, brown, or nearly white, it blends in with the sandy substrate upon which it hunts.

It may help to look for them at night. Arm yourself with a good headlamp or flashlight, held at the same level as your eyes. When the beam of light hits a wolf spider, the animal’s eyes will glint with a bluish-green shine. This technique works on other wolf spiders, too, and a female with young on her back looks like a diamond-studded stone. You will be surprised at just how populous lycosids are if you ever try this. I tried it on a lawn in south Texas once. I thought the grass was covered in dew. No, just wolf spiders!

Should you opt to seek the Beach Wolf Spider by day, try turning over driftwood and other debris on the shore. The spiders hide in such situations by day; they may also dig burrows in the sand, so look for that as well.

Despite being a swift, muscular hunter with excellent vision, Arctosa littoralis is not immune from its own predators. Several species of spider wasps in the family Pompilidae are recorded as using the Beach Wolf Spider as food for their larval offspring. Priocnemis cornica, Ageniella conflicta, and Anoplius apiculatus are among the pompilids that prey on Arctosa littoralis.

Summer is here, and vacation time is upon us. Consider looking for the Beach Wolf Spider and other seashore invertebrates during your next leisure trip to the beach. Don’t forget to pack your sunscreen and shades, though.

Wasp Wednesday: The Wasp Tree Part II

Last week I wrote about a single, blooming Saltcedar tree (Tamarix sp.) that was attracting a great diversity of insects, especially wasps. Well, after spending several more days at that (introduced, invasive) tree, I can add to the list significantly.

The butterflies alone now include Checkered White, Orange Sulphur, Dainty Sulphur, Gray Hairstreak, Acmon Blue, Reakirt's Blue, Painted Lady, American Lady, Variegated Fritillary, American Snout, Common Checkered Skipper, Common Sootywing (image above), and Uncas Skipper (identification tentative). Bees include the following families: Colletidae, Apidae, Megachilidae, and Halictidae.

The following list of wasps will be the final one. I will amend it as I make more specific identifications, and/or add new species during future forays to the tree:

• Argidae: Argid sawflies
• Braconidae: Braconid wasps
• Ichneumonidae (Ichneumon wasps)
• Chalcididae (Chalcid wasps):
• Brachymeria sp. (chalcid wasp)
• Leucospidae (Leucospid wasps):
• Leucospis sp.
• Chrysididae: Cuckoo wasps
  
  
• Scoliidae (Scoliid wasps):
• Campsomeris sp.
• Trielis octomaculata
• Tiphiidae (Tiphiid wasps):
• Myzinum sp.
  
  Myzinum male
  
  Myzinum female
  
• Mutillidae (Velvet ants):
• Dasymutilla sp.
• Vespidae (social wasps, mason wasps):
• Polistes dominula (European Paper Wasp)
• Polistes aurifer (paper wasp)
• Vespula sp. (yellowjacket)
• Eumenes sp. (potter wasp)
• Euodynerus spp. (mason wasps)
• Parancistrocerus? sp. (mason wasp)
• Pompilidae (Spider Wasps):
• Hemipepsis ustulata (“tarantula hawk”)
  
  
• Cryptocheilus sp.
• Anoplius spp. (spider wasps)
• Poecilopompilus interruptus (spider wasp)
• Sphecidae (Sphecid Wasps):
• Sceliphron caementarium (Black & Yellow Mud Dauber)
• Chalybion californicum (Blue Mud Dauber)
• Sphex lucae (katydid hunter)
• Isodontia elegans (grass-carrier wasp)
• Prionyx spp. (grasshopper hunters)
• Podalonia spp. (cutworm hunters)
• Ammophila juncea (caterpillar hunter)
• Ammophila wrightii (caterpillar hunter)
• Crabronidae (Crabronid Wasps):
• Sphecius grandis (Western Cicada Killer)
• Tachytes spp. (sand-loving wasps)
• Bembix sp. (sand wasp)
• Stictiella pulchella (sand wasp)
• Steniolia elegans (sand wasp)
  
  
• Bicyrtes sp. (stinkbug hunter)
• Astata sp. (stinkbug hunter)
• Dryudella sp. (true bug hunter)
• Stizoides renicinctus(image below, blog coming soon)
  
  
• Oxybelus sp. (fly hunters)
• Clypeadon sp. (harvester ant hunter)
• Aphilanthops sp. (“ant queen kidnapper”)
• Philanthus gibbosus (“beewolf”)
• Philanthus ventilabris(“beewolf”)
• Philanthus spp. (“beewolves,” at least two other species)
• Cerceris spp. (weevil wasps)
• Eucerceris sp. (weevil wasp)

All of the above were found either on the tree or in very close proximity. Male wasps take advantage of the fact that females will seek nectar at an isolated shrub and then create territories around it which they defend from other males. I found this was especially true of Tachytes and Philanthus, but I observed other wasps (and flies, too), mating on or close to the tree.

I have put together a “set” of images on my Flickr photostream entitled “Wasp Tree” that illustratse more of these insects. It is an ever-growing set, so please visit often. Thank you.

Spider Sunday: Mother Wolf Spider

Last Sunday was Mothers’ Day, but if you will forgive me I would like to pay tribute to arachnid mothers today. During my trip to South Carolina in early May, I had the occasion to momentarily observe a large female wolf spider of the genus Hogna on the afternoon of May 6, 2012. She had an egg sac and was living in a burrow on a wooded embankment adjacent to a road. I had stopped along with members of the Dragonfly Society of the Americas to look around a stream for dragonflies and damselflies. Descending the steep slope to get to the watercourse, another member of the party spotted the spider.

The arachnid was out of her burrow and standing on a network of threads just outside its entrance. The footfalls of others caused her to dash back into her refuge and I thought I’d seen the last of her.

I waited patiently next to her lair and was surprised when she returned to the lip of the burrow shortly. I was hoping she would climb back out for more photo opportunities, but instead she did something remarkable. She turned around inside her burrow and backed out to the entrance.

Why would a large wolf spider, with quite excellent vision, and perfectly capable of defending herself with her fangs, choose to present her vulnerable abdomen, and the egg cocoon attached to it, to potential lurking enemies? The only logical explanation that came to mind was that she was sunning her egg sac.

Indeed, there was filtered sunlight streaming through the forest canopy in the late afternoon: not too intense as to cook the ova within her silken package, but warm enough to help incubate the eggs. Still, had she not repeated this behavior, turning around at one point to make sure no threat was present and then backing out again, I’m not sure I would have believed what I was seeing.

It turns out this kind of behavior is not unheard of in other wolf spiders. Studies of Pardosa wolf spiders of two species revealed that at least one of them seeks open areas in which to expose the egg sacs to the sun (Buddle, 2000).

Had I been able to return to the site day in and day out, I would have eventually witnessed the mother spider cracking open her egg sac, allowing the newly-hatched spiderlings to emerge. Wolf spider babies crawl from the egg sac onto their mother’s back, completely covering her abdomen and sometimes much of her cephalothorax as well. She will transport the youngsters until their next molt, after which they disperse to live freely on their own.

Such devoted parental care is considered uncommon among spiders, but the more we learn the more the picture changes. There are even some female spiders that die immediately after their spiderlings hatch, offering their bodies as their offspring’s first meal.

A piece of long-standing advice is to “stop and smell the roses,” but it also pays to stop and observe animals, too. Science knows very little of the lives of most organisms that are not economically important, be they food sources or pests. Who knows what could come from your own casual observations of the insects, spiders, and other wildlife that share your yard, garden, and neighborhood park?

Source: Buddle, Christopher M. 2000. “Life History of Pardosa moesta and Pardosa mackenziana (Araneae, Lycosidae) in Central Alberta,” The Journal of Arachnology 28: 319-328.