Festive Parasites

Mistletoe is a classic Christmas decoration, which has always struck me as rather odd, considering that all varieties of mistletoe are parasitic plants. Depending on how bad the infestation is, mistletoe is quite capable of killing its host plants.

There are many types of mistletoe (117 species globally, 5 species of dwarf mistletoe are common in Montana). While mistletoe have many different host plants, around here our mistletoe varieties tend to be specialists on conifers – I’ve spotted some local Western Dwarf Mistletoe, generally found on Ponderosa Pines.

As for why we associate mistletoe plants with kissing?
They’ve been plants of spiritual importance for quite some time. And with that come many attempts at medicine… don’t try these at home, folks.

It’s easy to see why folks thought mistletoe might help fertility, though – Europe’s common mistletoe is an evergreen plant. It’s easy to find flourishing, clearly healthy and alive, even when all the deciduous trees are leafless. And think of how much more special the mistletoe would be thought, if it came from a type of tree held to be sacred, such as an Oak or an Ash.

The Roman historian Pliny the Elder claimed that Druids used mistletoe gathered from sacred oak trees in their rituals, though there’s little enough proof of that… it’s a long time back, the druids didn’t keep written records, and Pliny isn’t without error. Similarly, in northern Japan, the Ainu people used mistletoe gathered from their sacred willow trees to try to encourage fertility, as well as cure ailments.

In the great Roman epic, the Aeneid, the hero Aeneas is told to carry a golden branch of mistletoe with him on his journey to the underworld, so that he’ll be allowed to return to the surface world again. When there, he speaks with the dead, notably his father, and hears stories of how the Caesars will be his descendants.

However, it’s most likely that mistletoe’s connections to our holiday festivities come out of its ties to Norse mythology.

There’s a legend that the queen of the Norse gods, Frigga, went through all the world, making everything promise that it would not hurt her son, Baldr. You see, Baldr had recently begun to have visions of his death, and it is said that even gods find death a concerning prospect.

Now Baldr was a god of summer, beauty, and peace – best loved of all the gods. All the world pledged their love for Baldr. Stout oak and ash trees promised that their wood would never harm Baldr, stone and metal, beast and people alike. All pledged that they would not harm Baldr.

Loki, troublemaker of the gods, disguised himself as an old woman, and coaxed Frigga until she revealed the one thing she didn’t ask this of – mistletoe. She thought it too young, too weak a plant to harm Baldr, and hadn’t worried about asking it.

After hearing this, Loki journeyed east from Asgard, home of the gods, until he came to the forests where mistletoe grew. There he found mistletoe, and taking a particularly healthy plant, fashioned it into a throwing dart, and came back to the gathered gods celebrating Baldr’s invulnerability.

To test Baldr’s invulnerability, the gods held a celebration, and tried to harm Baldr with various weapons, lightly at first, then with more grievous and more grievous attacks. They delighted when nothing could harm Baldr, and believed that he had successfully cheated his visions of death.

At the outskirts of the gathering stood Hodr, Baldr’s blind half-brother. Another god of the seasons, Hodr was a god of winter, and surviving dark and harsh times. Loki asked Hodr why he wasn’t joining in the celebrations, and Hodr replied that he didn’t have a weapon to use against Baldr, and even if he did, he couldn’t see to use it properly. Loki offered to help Hodr join in the fun, gave him the dart of mistletoe to throw, and even helped guide his hand… When Baldr was struck, and mortally wounded, Loki made himself scarce, leaving poor Hodr to be executed for the murder of his brother.

The tale runs on, but the gist is that the Norse gods were unable to retrieve Baldr from the underworld. His mother, Frigga, wept, and her tears became the mistletoe berries. As Frigga was a goddess of love, marriage, motherhood and all things associated, mistletoe berries gained importance in treating infertility…

Not that I’d suggest you try to do so. Most mistletoe varieties are somewhat toxic.

Ask The Entomologist

Ichneumonid wasps, imposing allies

Last Thursday I saw this lovely Ichneumonid wasp (pronounced ICK-new-mon-id, from Greek “Ιχνευμων” which means “Tracker”). Most of the time I see Ichneumonids, they’re on the sides of trees, ovipositing (laying eggs) in boring insect larvae. This one’s behavior was very odd indeed.

An Ichneumonid wasp, Pimpla pedalis, oviposits into a newly split piece of Douglas Fir.

As you can see, this particular Ichneumonid wasp was laying her eggs inside a freshly split piece of Douglas Fir … or rather, inside a boring insect inside the Douglas Fir. Curious to see what insect she was laying her eggs inside, I peeled away layer after thin layer of wood …

Uncovering the beetle grub (at left, mid-height) the wasp laid her eggs in.

… And after an inch and a half of wood was removed, exposed a boring beetle grub. This is a Jewel Beetle grub, a member of family Buprestidae. These beetles can be lumber pests, though they’re unlikely to damage treated wood. While none of our Montanan Jewel Beetles are quite as bad, the Emerald Ash Borer has been devastating to ash trees throughout eastern North America.

There it is, a Buprestid beetle grub, just to the left of the burrow it gnawed in the wood.

I have very fond childhood memories of Giant Ichneumonid wasps. Most Sundays, my family would go to the arboretum of South Dakota State University’s then-public gardens. Among my favorite things there were some large multi-trunked cedars, which, in autumn, attracted some very large wasps. Presumably, the cedars also had very large wood-boring larvae that the Ichneumonids were parasitizing. Despite being a typical small human, making noise, climbing trees, and being generally bothersome, the Ichneumonid wasps never showed any sign of interest in me.

While their large stingers and stinger sheaths look quite formidable, Ichneumonid wasps very rarely sting mammals or other large animals. Unlike typical colony-living wasps and bees, Ichneumonid stingers are almost exclusively used for laying eggs inside of host insects. Eventually the eggs hatch, and the baby wasps eat the host insect from the inside out. Parasites that always kill their hosts are called parasitoids (think of the Xenomorphs from the Alien movies).

Fortunately for us, in addition to not stinging us or our pets, Ichneumonid wasps are also great at controlling garden pests. They take out a variety of garden pests (tomato hornworms, cabbage worms, etc.) as well as lumber pests (long-horned beetles, jewel beetles, bark beetles, etc.).

All in all, they’re neighbors I’m quite glad to have.

Ask The Entomologist

Louse flies

It’s autumn. Among the many little signs of this are the appearance of Western Deer Keds, or louse flies, as they’re often called. As I was walking in the woods this past week, a number of them flew about me, a couple landed on my hand and ran up and down my arms. A poor life choice for them, as they were swiftly collected.

Louse flies are members of family Hippoboscidae, and are best known for their very odd reproduction. They have their young one at a time, much like us humans. Females fertilize a single egg from stored sperm, the egg then hatches inside the mother fly’s reproductive tract. The resulting maggot nurses from a “milk” gland and molts several times inside the uterus. After about a week of this, the mother fly gives birth to a large late-stage maggot. In the case of the Western Deer Ked, the mother generally does this where the deer beds down for the night.

Liptoptena depressa, a deer ked, courtesy of my in-laws’ dog (an unsuitable host).

The late-stage maggot pupates immediately. After emerging from its pupal case as an adult in the fall, the new adult louse fly will take off in search of a suitable host. Once it finds a host, it will start feeding on blood, shed its wings, and will remain on the host until its dying day. Western Deer Keds can survive on Mule Deer, White Tailed Deer, Elk, and Moose. They may try to feed on other species – they can certainly bite. But they won’t be able to survive for long off of their proper hosts.

Keds are best known as livestock pests – sheep keds are somewhat famous for the economic damages they can inflict. Native to Europe, sheep keds immigrated with humans, and are present across almost all of North America and much of South America, as well as parts of Africa, Asia, and Australia. While sheep keds have been reported, there is not good evidence that they can survive long on Bighorn Sheep or Mountain Goats.

If you hunt turkey, and have tried for the “Grand Slam” you might have encountered turkey keds in the American southeast as well. There’s several species of turkey keds, but to the best of my knowledge, none have made it west of the Rocky Mountains yet.

Have you met louse flies before? When, and on what?