The woodpecker and the weevil

It’s unusual to see Downy Woodpeckers foraging on herbaceous plants in the middle of a prairie landscape, even if the flower stalks do reach 5-6 feet tall.  But the mature seed pods of Common Mullein may harbor a feast of insect larvae that Downy Woodpeckers have learned to harvest.

downy woodpecker on Common mullein

This Downy female spent quite a long time exploring every bit of all the Common Mullein flower stalks on a small patch of prairie. She worked around the bottom half of the flower stalks, then flew to the next stalk to start another search.

Common Mullein is a fuzzy-leaved biennial weed, introduced from Europe.  During its first year of growth, it produces a large rosette of furry leaves, followed by one to several tall spikes of small yellow flowers the following year.

downy woodpecker on mullein

Only a few small, yellow flowers open each day (and they last just one day), but the woodpecker isn’t interested in insects on the flowers.

Mullein is famous for its seed production — putting out as many as 175,000 seeds per plant.  But the woodpecker isn’t interested in eating the Mullein seed either.  But that much seed in one place becomes highly attractive to insects, like Mullein Weevils, whose larvae specialize in devouring mullein seeds.

downy woodpecker on common mullein

Each of the knobby seed capsules that surround the flower stalk harbors as many as 500-600 seeds. A weevil larva develops inside one seed capsule where it consumes 100% of the developing seeds, and finally pupates there. 

The lower and middle thirds of the Mullein flower stalk seem to suffer the heaviest infestation of weevil larvae, with the top being relatively weevil free.  In all, weevils destroy/consume about 50% of the mullein seeds, which still leaves a lot of seed production from just one plant (~80,000!).  But without this semi-effective control of mullein seed production, that species would be a lot more invasive.

Then as seeds are maturing, along come Downy Woodpeckers who probe the seed capsules for larvae and pupae, thus keeping the weevil population in check. A nice system of biological control at a couple of different levels.

A fly to love…

Most flies seem kind of ugly to me, or perhaps it’s just their behavior I dislike —  buzzing around my head and occasionally biting.  But here is a fly to admire, and in fact to cultivate in your garden.

A easily recognized fly, with its white scoop face, stubby antennae, red eyes, and bristly black butt.

An easily recognized fly, Archytas apicifer, performs a valuable service by pollinating the flowers of many plant species.

Not exactly beautiful, but striking in its features, with its white face, red eyes, and bristly black butt.  Archytas apicifer doesn’t seem to have a common name, but I’ll refer to it as White-faced Fly here.  It is a member of the Tachinidae family, a very large group (~10,000 species), all of whom are parasites on other organisms.  White-faced fly happens to be one of the larger species, about 1 inch in length, and a very fast and agile flyer.  The adults are fond of nectar and may be good pollinators.  I found them in great numbers on the Black-eyed Susans and Canada Goldenrod in my backyard.

On the Black-eyed Susans, the fly systematically explored every open disc flower by circling the flower head.

On the Black-eyed Susans, the fly systematically explored every open disc flower by slowly circling the flower head.  Its antennae project downward over a scooped out portion of the “face”, which makes me wonder what this curious anatomy is for. 

In contrast, when foraging on the Canada Goldenrod, the fly moved randomly, rarely spending more than a few seconds on any one frond.  Several species of bees were much more systematic in their search.  The difference could have something to do with proboscis or tongue length perhaps.

In contrast, when foraging on the Canada Goldenrod, the fly moved randomly, rarely spending more than a few seconds on any one frond. Several species of bees were much more systematic in their search. The difference could have something to do with proboscis or tongue length perhaps.

The larvae also perform a vital ecological service, as they parasitize some of the more noxious pest caterpillars — tent caterpillars, fall webworm, tomato fruitworm, corn earworm, and cutworms.  Adults lay their eggs on the underside of the host; when they hatch, the larvae burrow into the host and begin consuming it.  One less pest to worry about.

This shot provides a better idea of the fly's size relative to the central disc of a Black-eyed Susan flower.

This shot provides a better idea of the fly’s size relative to the central disc of a Black-eyed Susan flower.

Its features don’t inspire immediate affection, but the White-eyed Fly is a beneficial insect nevertheless.

what is black and white and red..in places?

When we were traveling in Turkey, I got a few chances to photograph some of the wildlife, featured in a recent post, but largely unidentified.  Thanks to one of my savvy fellow travelers who found an image of one of the creatures on Flickr, I now have a name for the caterpillar I saw.  It turns out the species also occurs in the U.S., even in Minnesota, where it was introduced on purpose to control a noxious invasive called leafy spurge. (Below, leafy spurge was one of the earliest plants to emerge last spring near my backyard.)

This little beauty…is the caterpillar of the Spurge Hawk-moth (Hyles euphorbiae), seen in one of its native lands (asian part of Turkey) on one of its natural food sources, perhaps Euphorbia lambii, the Tree Euphorbia.  The plant is native to the Canary Islands, but has been introduced everywhere in the world as an ornamental.

In fact these spurge bushes were crawling with caterpillars, and they were doing a fine job of trimming back the green vegetation to bare sticks.  Black coloration with white spots and red trim makes the caterpillars really stands out.  When streched out, you can see green segments between the black and white.

Typically such eye-catching coloration is a warning to predators that the prey is inedible at the least, or poisonous at the worst.  Its host plants, the euphorb species, are toxic, especially the leaves.  However, sea gulls have been observed to pluck the caterpillars right off the euphorb bushes growing near the sea shore, so perhaps their toxicity is mild.

The adult moth is quite attractive with well-defined brown patches on the forewings and pink coloration on the hind wings.  They are day-flying moths (like other sphinx moths), and exhibit hummingbird-type flight when visiting flowers, hovering near the flower heads and dipping their long coiled proboscis systematically into each flower.

Photo from: http://ukmoths.org.uk/show.php?bf=1986

After mating, females lay clusters of up to 50 eggs on leafy spurge plants, adhering them to the stems with a sticky gum substance.  Easy to see why the plants we saw on our hike were covered with maturing caterpillars.

Photo from: http://en.wikipedia.org/wiki/Hyles_euphorbiae

Even if the caterpillars defoliate the spurge, the plants seem to recover quite nicely.  Unfortunately, the moth’s introduction has not provided the biological control for leafy spurge that was hoped for.