If you look closely at the ground directly in front of this female Black and Yellow Mud Dauber wasp you will see the clump of mud that she has collected and rolled into a ball with her mandibles. This lump of mud will be carried back to the nest site in the wasp’s mandibles, and then used as building material to mold a cell. After making the mud cell, the wasp then goes and locates spiders, stings them (paralyzing but not killing them) and brings them back to the cell, into which she packs them. When the cell is sufficiently stuffed with spiders, she lays an egg and seals the cell with more mud. She makes and fills several of these cells and typically covers all of them together with a final layer of mud. When the wasp egg in each cell hatches, the larva has living spiders to eat that haven’t decomposed, due to the fact that they are not dead. Eventually the larval wasp pupates and the adult wasp chews its way out of the cell.
Having known since childhood that most insects have only one pair of antennae, imagine my surprise when I came upon a hornet on Queen Anne’s Lace that appeared to have two: a pair of slender, black antennae, and between them, a shorter pair of white ones. A bit of research revealed to me that in fact, these white “antennae” were actually the pollen sacs (pollinia) of an introduced and somewhat invasive orchid, Broad-leaved Helleborine (Epipactis helleborine).
Broad-leaved Helleborine is entirely dependent on insects to spread its pollen, especially wasps. It attracts them with nectar, which is said to have an alcoholic and narcotic effect which may help with the spreading of pollen, as an inebriated wasp is less likely to clean pollen off its body before leaving. Helleborine also produces a chemical which other plants produce and use to signal that they are being attacked by insects. It is used purely as a ruse by Helleborine, in order to attract wasps, Helleborine’s primary pollinators, who arrive to fend off other insects, and end up inadvertently collecting Helleborine’s pollinia.
Unlike the pollen of most plants, Helleborine’s pollen grains are so sticky that they cannot separate – thus, the entire package of pollen remains intact and is removed at one time. Wasps are capable of reaching the plant’s nectar without disturbing the pollinia, but cannot crawl out of the flower without striking against and detaching them and in so doing, getting them stuck to their heads. Can you find the pollinia in the insert photograph of a Broad-leaved Helleborine flower (which has not been visited by a wasp yet)?
Due to computer issues, Naturally Curious will resume posts next Tuesday, August 16.
If you research bald-faced hornet nests you will find that their average size is often compared to that of a football or basketball. The maximum size is said to be between 14 and 18 inches in diameter, and up to 23 or 24 inches in length. The pictured nest (which hung 20 feet above the roof of my house) measures 14 inches wide and 29 inches long – far larger than the average hornet nest!
This entire nest was built in roughly four months. It was started by a queen bald-faced hornet that, after emerging from hibernation this past spring, chewed some wood fiber, mixed it with her saliva and created a few brood cells surrounded by one or more paper “envelopes.” She laid an egg in each cell, and fed the hornet larvae insects which she first masticated into tiny bits. When the larvae pupated and emerged as adult workers, they assumed the duties of nest building, food collection, feeding the larvae and protecting the nest, while the queen continued laying eggs in horizontal tiers of cells. This ongoing activity produced a colony of anywhere from 100 to 400 workers by the end of the summer. Shortly before the first hard frost this fall, the queen left the colony and found a protected spot in which to spend the winter. When freezing temperatures arrived, the workers all died, leaving a nest that will never again be inhabited by bald-faced hornets. (Thanks to Nick Burnham, who ingeniously managed to collect the nest for me, and Gary Trachier for the photo.)
Horntails, also known as wood wasps, are non-stinging, wood-eating insects that lay their eggs deep within trees. Both male and female horntails have a pointed spine at the tip of their abdomen; females also have a long, slender ovipositor. (They get their name not from their spine or ovipositor, but from a knob (cornus) at the tip of their abdomen.)
Pigeon Tremex Horntails (Tremex columba) are active in late summer and early fall. A mated female inserts her ovipositor several inches into a dead or dying tree and lays an egg (where it is safe from most, but not all, predators). Along with the egg the adult horntail deposits some white rot fungus (Daedalea unicolor) which she stores in special abdominal glands. The fungus breaks down and softens the wood for the horntail larva to eat and is required for the successful development of the horntail. The larva typically begins consuming the soft, fungus-ridden wood around it, and then chews its way to the inner bark so as to provide a means of exiting the tree when it becomes an adult. The larva then returns to feed on inner wood. It completes its metamorphosis and emerges from the tree within a year as a winged adult horntail.
There is a parasitic wasp, the Giant Ichneumon Wasp (Megarhyssa macrurus), which possesses a long three-inch ovipositor capable of drilling into trees. There are several theories as to how this parasitic wasp detects the presence of horntail larvae deep within the tree. She may lay her antennae on the outside of a tree and pick up the vibrations of horntail larvae gnawing away in their wood chambers. Another theory proposes that the female wasp uses her antennae to smell the frass (droppings) of the horntail larva as well as the wood-softening fungus. Once she locates a horntail larva, the ichneumon wasp paralyzes it and then lays an egg on it. The ichneumon wasp larva feeds on the paralyzed horntail larva, consuming it completely within a couple of weeks. The ichneumon wasp then pupates and remains dormant under the bark until the following summer, when the adult emerges.
From the size of the chunks of sod that were ripped out of the ground in order to access this subterranean yellow jacket (Vespula sp.) nest, one can deduce that a black bear, not a striped skunk or raccoon, was the nocturnal visitor. Usually there is little intact nest left after a bear tears it apart in an effort to find yellow jacket larvae, but in this case, a portion of the paper nest remained. Apparently undaunted, even with frost in the air (signaling the demise of all the yellow jackets except young, fertilized overwintering queens), the workers lost no time in rebuilding their nest. Twenty-four hours after their nest was torn apart, the colony of yellow jackets had diligently chewed enough wood fiber to have replaced much of it.
Of the 2,000 kinds of galls found on North American plants, 800 different kinds form on oaks. One of these is the woolly oak leaf gall, produced by a tiny Cynipid wasp, Callirhytis lanata. This gall is usually attached to the mid-vein on the underside of an oak leaf, and looks like a ball of wool. It may be as large as three-fourths of an inch and is often bright pink or yellow in color, fading to light brown in the fall. Oak trees have lots of tannic acid in them (a defense which makes the tree unpalatable to herbivores), with the highest concentration found in oak galls. (The bitter taste is where the name “gall” originated.) It’s possible, since tannins are somewhat anti-microbial, high-tannin galls such as the woolly oak leaf gall may protect the larva against fungi and bacteria.