Saturday, August 18, 2012

Black and Yellow Argiope (Argiope aurantia)

A large, robust spider, the female Black and Yellow Argiope can attain a length of about 25 mm, the considerably smaller males, as is often typical among spiders, are only about 5 mm long. To date, a Cicada or Dogday Harvestfly is the largest prey I have ever seen one of these spiders take down.

The white zigzag pattern in many orb weaver's webs is called a stabilimentum, so called because at one time it was thought to stabilize the web. But experiments have shown that the stabilimentum – and the spider itself – reflect ultraviolet light. Since many insect's eyes are sensitive to the UV spectrum and flowers often reflect patterns visible in UV to attract insect pollinators, the current theory in vogue is that the stabilimentum and spider may act as lures to entice insects into the web. However, as adult Cicadas don't eat it's not likely this one was tricked into flying in the web – it was unlucky and simply blundered in.

A couple more views of this harmless, attractive arachnid.

Tuesday, August 14, 2012

Tricky Tick Trefoils, Flowering Fabaceae and Leafy Legumes

Magnificent in magenta, groups of eye-catching Tick Trefoil can be found blooming in sunny locations along the Moira River shoreline during the first week of July. After consulting the species accounts in my field guides and various Internet sources I decided that the plants' attributes were consistent with Showy Tick Trefoil (Desmodium canadense).

Growing all by itself in a much shadier shoreline area in mid-August, the stems and leaves of this Tick Trefoil are more delicate and much less hairy than the plants above, and the flowers have a different aspect. Is this a different species – Illinois Tick Trefoil (Desmodium illinoense) – or are the variances due to habitat?

Tick Trefoils are best distinguished by their loments (the pod-like fruits) so I re-visited the site where the plants in the photos above were growing, and unfortunately there was no sign of any fruits.

Regardless of which species this eventually proves to be it is definitely a beautiful and striking flower that stands out from the crowd.

Tick Trefoil are members of the family Fabaceae (a.k.a. Leguminosae) which includes the clovers (several species in our area), and economically important plants such as peas and beans. Another ubiquitous and showy legume which prefers the same riparian habitat as the trefoil(s) is the Groundnut (Apios americana).

The American Hog Peanut (Amphicarpaea bracteata) has somewhat less flashy flowers but is just as common; this vine flourishes in drier areas along the trail as well as the riverbank.

Originally native to Eurasia and Africa, Crown Vetch (Securigera varia) is planted on this side of the pond along roadside embankments and other areas that require erosion control. Since Fabaceae are symbiotic with nitrogen-fixing bacteria (rhizobia) in their root nodules they also have the added benefit of reconditioning and reclaiming poor soils. Considered an invasive species in some jurisdictions, this plant's pros outweigh its cons ... and besides, masses of Crown Vetch in bloom look nice.

In addition to improving soil fertility many Fabaceae species such as clovers and alfalfas are valued as livestock fodder. On the other hand, some – Bird's-foot Trefoil (Lotus corniculatus), for example – do have their down side. Every grazing animal is potentially the enemy of a plant, and in response many plants have evolved chemical defenses to deter hungry herbivores. Bird's-foot Trefoil's defensive weapon of choice is deadly prussic acid.

Trifolium pratense, better known as Red Clover ... but there are times when "Trifolium" seems to be a misnomer. I have often stumbled across several plants – White Clover and Alsike Clover as well as Red Clover – growing in a relatively small area with leaves sporting four or five leaflets.

And then there's this unusual specimen, where a good number of the leaves had four or five leaflets. Is this due to genetics? Or an abundance of nutrients?

The leaves all appeared discolored ... is this caused by some kind of disease, and does it have some bearing on the plant's multi-leaved growth form?

Curiouser and curiouser – a "green" Red Clover capitulum? No, it appears that the flowers (there were actually two on this plant, a different specimen and location than the multi-leaved one above) are replaced by tiny leaves! If this characteristic is theoretically heritable the plant won't be passing it on to the next generation ... not by means of this particular "flower", in any event.

Friday, August 10, 2012

Sharing the Risks and Dividing the Dangers

A quote from the preamble to the U.S. Constitution sums up the idea of Müllerian mimicry very well – "We the people ... in order to ... provide for the common defense, promote the general welfare ..."

Müllerian mimicry is named in honour of the German naturalist Fritz Müller, who first observed and offered an explanation for the phenomenon. Simply put, several species, not necessarily related, that have predators in common will also tend to mimic each other and share aposematic colors or warning signals. Of course, unlike the U.S. model there's no conscious or intelligent decision to co-operate, and the mutations that eventually give rise to a given defensive game plan are random – but the process of natural selection is not. A given shared color scheme benefits and promotes the survival of all the individuals within the species that share it, and it's survivors that (naturally!) hand their genes down for another roll of the dice to the next generation.

Members of the order Hymenoptera that can sting tend to exhibit bold black-and-yellow stripes. A child, a bird, or a frog that has been stung by a Honeybee will likely remember the painful experience and in future also avoid a Bumblebee, a Paper Wasp and a Mason Wasp – the individual Honeybee (a non-reproductive worker in any event) loses, but its relatives and the other Hymenopteran species gain a measure of immunity from predation.

Beetles belonging to the family Coccinellidae, better known as Ladybird Beetles or Ladybugs, secrete toxic alkaloids to discourage predators, exuding fluid from their leg joints if threatened. The colors and patterns of many species are variations on a similar black-and-red theme, and not surprisingly, their family name is derived from the Latin word for scarlet.

Three-Banded Lady Beetle (Coccinella trifasciata perplexa)

A mating pair of Polished Lady Beetles (Cycloneda munda)

Convergent Ladybird (Hippodamia convergens)

Glacial Ladybird (Hippodamia glacialis glacialis)

Milkweeds produce cardiac glycosides to ward off insects, but over time a diverse assortment of insect species have adapted and appropriated the milkweed's chemical defense for their own protection. Such insects sequester the toxins in their own bodies and boldly advertise their noxious natures with a combination of showy black and red/orange colors.

The well-known Monarch (Danaus plexippus)

Small Milkweed Bug (Lygaeus kalmii)

Large Milkweed Bug (Oncopeltus fasciatus)

Larvae of the Milkweed Tussock Moth (Euchaetes egle) ... a group of these caterpillars can annihilate a leaf, within a short time there's little left but the veins and frass.

Red Milkweed Beetles (Tetraopes tetrophthalmus) – their scientific name, derived from Greek, means four eyes. Apropos, as their antennae arise in a manner that divides their compound eyes into a pair of eyes above and below the antennae. And in the background it looks like there's an exception to the black-and-red milkweed color rule, a tiny Monarch caterpillar.

Another image of the Monarch larva, and that's nature for you ... as soon as you think you've found a rule or underlying logical principle, there's a departure or deviation that challenges your assumptions as to how things work.

On the other hand – Monarch caterpillars aren't toxic from the get-go when they hatch, they acquire their bad taste over time as they consume milkweed leaves. It's been my observation that the yellow, white and black stripes on the tiny first instar larvae are indistinct and blend together to form green, thus camouflaging the caterpillars while they are still vulnerable to predators. And the strongly marked later instars do in fact possess the black-and-yellow aposematic warning scheme common to many Hymenoptera. So it seems that the Monarch participates in two different Müllerian defensive strategies throughout its life cycle.

Wednesday, August 8, 2012

Coleopteran Conundra

The change of form among insects that undergo complete metamorphosis is astounding, and it's difficult to believe that the egg, larva, pupa and adult are really one and the same insect.

Pupae are often thought of as a dormant and inactive but these little guys, found in moist soil under a rock along a riverbank, were quite lively when disturbed. Given the habitat, a species of diving beetle seemed to be a reasonable guess but I really had no idea as to family, let alone genus or species, so I submitted the images to BugGuide.Net for an ID.

Only so much information can be gleaned from a digital image. My camera is limited when it comes to macro shots and I don't know what the criteria are for identifying pupae in any event (in other words, which features are best to photograph?). So it seemed like a good move to take a couple of specimens home and see what kind of a beetle would emerge ... and hoping that whatever species this proved to be didn't overwinter in the pupal stage. I wasn't disappointed; the next day there was an adult Water Scavenger Beetle in the container, and not long after I posted the photos to BugGuide.Net one of the experts narrowed the ID down even more.

It seems that the keel on the ventral side is significant and my mystery pupae belong to the genus Tropisternus.

Pretty in pink – whilst grubbing (pun intended) around under the riverside rocks and logs I found another beetle pupa and invited it to stay at my home for a time as well. I'm guessing that this is a Firefly, family Lampyridae ... time will tell. The larvae and pupae of some species are bioluminescent; I experimented in a dark room and found this one is not.

Four days later the adult beetle can been seen through the pupal case. The pupa is quite lively if disturbed and it's probably not much longer until eclosion (emergence) of the adult ...

Five days and counting ...

Development proceeded normally the following day but two days later it was obvious that the pupa had perished; there appeared to be something like a fungal growth on the exoskeleton. So what kind of beetle this – other than family Lampyridae, probably genus Photinus – will remain a mystery.

Looking like an alien from a sci-fi movie but nothing like the adult form it will eventually assume, this Predacious Diving Beetle larva (Dytiscus sp.) was sharing a beaver pond with the Eastern Newts photographed in the spring. With its needle-like jaws and easily 50 mm in length, the "Water Tiger" is beyond a doubt the top insect predator in its corner of the world and a newt's – not to mention a lot of other aquatic denizen's – worst nightmare.

An adult female Predacious Diving Beetle, note the grooved elytra. A rather striking change in appearance! Who would guess, without studying their life cycle and observing the changes, that the insects in these two sets of images were the same species?

The smell of carrion somewhere nearby gave a clue to the possible identity of these millipede-like larvae.

The radically different colors and profile of the adult American Carrion Beetle (Necrophila americana), one of nature's clean-up corps.

Ladybird Larvae offers a few more examples of the dramatic dissimilarities throughout the stages of a beetle's life.

The parallel striations running transverse to the length of the elytra help separate genus Colymbetes from other similar species of Dytiscid beetles. The smooth streamlined profiles of diving beetles never cease to amaze me ... so smooth that the males of some species have suction cups on their first pair of legs to hold onto the females during mating.

Rather than take pictures on the ground under poor light conditions, I let this beautiful, iridescent Carabid beetle – a Vivid Metallic Ground Beetle, genus Chlaenius – climb about on my hand until it was docile so I could turn to an angle to best display its colors. It's a good idea to handle Carabid beetles with caution; their colors may be aesthetically appealing but the foul smelling, noxious chemicals produced by many species to deter predators are definitely not, so it's best not to alarm the insect ...

Metamorphosis, mimicry and camouflage, chemical defenses, evolution, natural selection and how the myriad forms of life on our planet adapt to their ever changing circumstances, there's always something new to discover in the world of nature ... to quote one of my favorite science-fiction characters it's ... "Fascinating" ...