look-alikes (and not)

The Grass Lake slough at Snail Lake regional park is teeming with butterflies, especially Monarchs, which may be congregating here for their southward migration.  The Monarchs especially seem to like the meadow blazing star and don’t even mind sharing it with a lot of other butterflies, bees, etc.

The number of flowers present on meadow blazing star is one reason that butterflies congregate on it. The fact that it provides a lot of nectar at a time (late August) when butterflies are migrating is another.

Plenty of nectar to go around for Painted Ladies (also migrating by the thousands in late summer), Monarchs, bumblebees, honeybees, and a few stray beetles.  The orange, black, and white pattern of the Painted Lady is similar to that of Monarchs, but they are not mimics and the two are easily distinguished from one another.

But one of the many Monarch butterflies I photographed wasn’t a Monarch, but a Monarch mimic, the Viceroy, and these two unrelated species ARE difficult to tell apart.  Can you spot the difference(s)?

Both species exhibit the bold orange and black pattern on the wings as well as the pattern of white dots on the black head and thorax of the insect. 

The biggest difference in coloration of the two species is the bold black horizontal (sort of) stripe on the hind wing of the Viceroy, seen from above or below.  The thick black lines on the hind wing of the Viceroy are similar to those of a female Monarch but are much bolder than the male Monarch’s, which also has a distinctive dot on each hind wing.  In addition, Viceroy butterflies are smaller in size, only about 2/3 the size of a Monarch.

But where Monarch caterpillars grow up eating milkweeds containing poisonous cardiac glycosides which they sequester in their bodies (and wings), Viceroy caterpillars eat willow, poplar, and cottonwoods — not at all poisonous. Bird predators find Monarch butterflies extremely distasteful and will regurgitate or spit them out. Viceroy butterflies that most closely resemble their poisonous cousins in coloration are better protected from predation, and thus, the mimics survive to reproduce.

And then there are these two, apparently dissimilar butterflies, flitting around the same plants, often displacing each other from the same flowers.

The Eastern Tiger Swallowtail comes in two colors: yellow and black, and black.

Not at all look-alikes, in fact, color-wise, they couldn’t look more different, except for the pattern of white dots around the margin of the wings and the distinctive iridescent blue splashes of color on the back end of the hind wings.  So, what’s going on here?

Male Eastern Tiger Swallowtail butterflies are almost always yellow with black stripes.  Females on the other hand vary between yellow morphs and black morphs.  And, the black morph is more commonly found in the southeastern U.S. where a similar-colored, poisonous and unpalatable Pipevine Swallowtail butterfly occurs.  These are the “look-alike” models for the Tiger Swallowtail (and other Swallowtail butterfly species) to copy.  Interestingly, the proportion of female black morphs of the Tiger Swallowtail is higher in southern populations because of genetic (sex-linked) process that makes black morph females produce mostly black morph females, and yellow females produce mostly yellow females!

Bottom line:  you have to look closely when identifying a butterfly, because it might be a mimic!

Comparison of three common swallowtail butterfly mimics and their model, the Pipevine Swallowtail. From butterfliesathome.com

Why are some egrets and herons white?

More specifically, why are juvenile (first year) Little Blue Herons white when their parents are such a dark slate blue color?

These and many other perplexing questions arose as we walked around Blackpoint Drive wildlife refuge in Cape Canaveral, Florida last week, at the end of our 11-day cruise from Montreal to Florida through the St. Lawrence seaway and Maritime provinces of Canada.

First, the startling contrast between juvenile and adult Little Blue Herons:

Adult Little Blue Heron, St. Croix Island

Adult Little Blue Heron, taken on St. Croix Island, distinguished by its slate blue legs and plumage, slightly purplish head feathers, and strongly bi-colored bill with a black tip.

Juvenile Little Blue Heron

Juvenile Little Blue Herons have the same bi-colored bill as the adults, but an all-white plumage and gray-green legs and feet.

What is the advantage of being white, or is there an advantage, especially in this species?

Juvenile Little Blue Heron

Juvenile Little Blue Herons resemble Snowy Egrets, or Cattle Egrets, or even Great (White) Egrets, so you have to look carefully to see which species they are.

Considering the natural history of the bird gives us some clues:  Little Blue Herons (LBHs) can be found year-round along the Gulf of Mexico and the Caribbean islands, they winter in Mexico and Central America, and breed in marshy areas throughout the southeastern U.S., usually in exposed, full sun locations.  In other words, they hang out in some hot, humid places, where being white is an advantage.  And in fact, white-colored birds reflect about 80% of the incoming radiation, which helps them stay cool in these hot habitats.  So, thermoregulation is one advantage of being white for the juvenile LBHs.

But here is another advantage:

Little Blue Herons, Snowy Egrets, and White Ibis, Cape Canaveral, FL

Juvenile Little Blue Herons like to hang out with similar-sized Snowy Egrets and White Ibis.  Foraging techniques of the other two species scare crustaceans and small fish toward the usually solitary, patiently waiting predators, the LBHs.  In this location, a juvenile LBH on the right is being chased away by an adult LBH while Snowy Egrets and White Ibis forage in the shallows on the left.

Safety in numbers is certainly an advantage for white birds of mixed species, but so is being able to capitalize on all the critters fleeing from other wading predators.  Some studies have shown that inexperienced juvenile LBHs enjoy as much success in their foraging attempts as adult birds who typically forage by themselves.

Adult Little Blue Heron, St. Croix Island

Little Blue Herons are usually solitary, sit and wait hunters.  They stand, neck outstretched, head down, or walk very slowly through shallow water or marshy puddles to find their prey.

Foraging studies on wading birds have determined that more active pursuers like Snowy Egrets encounter more prey, but have lower capture efficiency than stalkers like the LBH.

For Little Blue Herons, there are several advantages for being white, especially in their first year of life.  A better question might be, why are the adults so dark?  Any thoughts?

Here’s a possible hint:

Adult Little Blue Heron driving off a juvenile LBH

The adult Little Blue Heron driving off a juvenile casts a very dark shadow on the water…

Another bee mimic

Flower gardens are in bloom up and down the street, so I took a stroll to see what insects I could find on the rich diversity of flowers available right now.  There should be lots of bees gathering nectar and pollen from those flowers, right?

robber fly-bumblebee mimic

robber fly-

Is this a bumblebee?  Hmm… doesn’t look quite right.

bumblebees-and-dahlias-

Well, let’s compare these two bumblebees on a dahlia with that “bee” above.

The bumblebee pretender has only one pair of wings, big bug eyes, no pollen baskets on those big hind legs, funny looking feet (not bee-like), and a big proboscis that sticks straight out from its head rather than straight down, like a bee’s would.  It looks like a bee, flies like a bee, even hums like a bee — but it’s a fly!  More specifically a robber fly, a predator of bees and other flying and crawling insects.

robber fly-bumblebee mimic

A closer look at this robber fly-bumblebee mimic nicely shows off his predatory apparatus.  Robber flies dart out and catch prey with their spiny legs, then ram their proboscis right into an unsuspecting insect, inject some salivary enzymes into the prey via the proboscis, and slurp back the digested material.

Laphria-Myrmecos blog-Alexander Wild

A bee-mimicking Robber Fly (Laphria species) attacks and consumes a honeybee. Photo by Alexander Wild.

There were only a couple of bees in the garden today — many fewer than I would have expected.  But there were lots of bee mimics, hoverflies, robber flies, and others.  Where are all the bees?  Do you see bees in your garden?  Look closely, what you’re seeing could be bee mimics.

Not a bee…or a wasp

Each day I go out in the garden to look for bees, and each day I find only flies, damselflies, and dragonflies.  So many flowers, no bees.  Even the bumblebees have deserted the garden, it seems.  Finally, I spied something yellow and black, about the size of a honeybee, not really buzzing, but definitely very interested in the pollen.

Very short stubby antennae, a single pair of wings, and an almost hairless body mean this is a fly, not a bee.

Very short stubby antennae, a single pair of wings, and an almost hairless body mean this is a fly, not a bee.  It’s a bee-mimicking syrphid fly.  These are good insects to have in the garden — the adults are good pollinators, and their larvae are predatory, consuming lots of aphids and other pests.

Syrphid flies eat a lot of pollen, but they also do a good job of transferring it from one flower to the next as their head and tongue comes into contact with the anthers.

Syrphid flies eat a lot of pollen, but they also do a good job of transferring it from one flower to the next as their head and tongue comes into contact with the anthers.

If I were naming insects I would call this "vacume fly" because his long proboscis ends in a stubby tube

If I were naming insects I would call this one, “vacume fly” because his proboscis ends in a stubby cylinder, just like the end of a vacuum hose.

There are some very small (< 1/2 inch) wasps flitting about in the garden, but they rarely sit still enough on a flower to photograph.  One caught my eye, though, because it did sit very still.

A closer look reveals that this, too, is not a bee or wasp, but a wasp-mimicking clearwing moth.

A closer look reveals that this, too, is not a bee or wasp, but a wasp-mimicking clearwing moth, about the same size as the tiny black wasps I was seeing.  No more than a 1/2 inch long, but with a very distinctive behavior while sitting — flicking that fringed “tail” slowly up and down.

The clear wings, dark purple body with yellow stripes, and fan tail were good hints about where to start looking on BugGuide.net.  I think this is probably a Eupatorium Clearwing Moth, whose larvae like to feed on the roots of Joe-Pye weed.  Oh great!  I just planted some of that in the garden last summer.

It’s interesting how many insects have copied that yellow and black body coloration of the stinging Hymenoptera.  I wrote about this mimicry pattern last year, so I won’t repeat myself here.  But if you would like to read more….click here.

It’s all in the spots

White Admiral or Red-spotted Purple — do those sound like the same butterfly?  Well, they are, strangely enough.  Although once considered separate species, they are in fact the same one that occurs from Alaska to Texas through-out the central and eastern U.S.

In the north they look like this, and are recognized as White Admirals.

By D. Gordon E. Robertson (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

By D. Gordon E. Robertson (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)%5D, via Wikimedia Commons

In the southern part of their range they look like this, and are recognized as Red-spotted Purples.

Note absence of white spots and iridescent blue color on the upper surface of the wings

Note absence of white spots and iridescent blue color on the upper surface of the wings. The underside of the wings have many orange spots. Taken two years ago in my backyard.

The other day, an individual that truly looked like an intermediate between these two forms showed up to have a drink from the milkweed flowers.

Some white spots definitely visible, along with a lot of orange on the underside of the wings.

Some white spots definitely visible but not as large and well delineated as the northern White Admiral.  There is also a lot of orange on the underside of the wings.

But also some of the iridescent blue color, especially on the hind wing.

But also some of the iridescent blue color, especially on the hind wing.

Wikipedia calls this species polytypic.  This intermediate coloration seems appropriate for an individual that is somewhat in the middle of the entire geographic range where you would expect hybridization of the northern and southern color morphs.

The Red-spotted Purple form is actually a mimic of the poisonous Pipevine Swallowtail, so there may be advantages to keeping some of that southern coloration in this mid-latitude geographic area.