Sunday, July 28, 2013

The Baltimore Checkerspot Returns

A Baltimore Checkerspot Butterfly nectars on Indian Hemp
We've had our first good Baltimore Checkerspot season in at least 5 years. Lately They've been spotted in various meadows around the nature preserve. Its interesting how some species, like the Baltimore, can become so rare even though their available food supply (larval food plants) varies so little year to year. Turtlehead is the traditional food plant for the species and it has only expanded in the past 12 years - both on its own and due to our restoration efforts. 
Turtlehead is the traditional host plant of the Baltimore Checkerspot
Turtlehead occurs in wet meadows and along stream sides
The Baltimore also utilizes English Plantain as an adopted food plant. This alien weed is ubiquitous in fallow fields, suburban yards and so called "waste places". Though the ability to feed on such a prevalent plant could only be considered as good news, it still has not resulted in making the checkerspot very common.
The Baltimore is one of our most distinctive butterfly speices
Baltimores mating in one of the upland meadows

With the ability to inhabit both low land swamps (the domain of turtlehead) and dry upland fields  (where plantain often dominates), the Baltimore may be encountered in a range of diverse habitat settings. At the preserve, it has been the wetlands where they occur most reliably - and when the population contracts, it's most often the wetlands that hold the last remnant of the population.
A female Checkerspot with its abdomen swollen with eggs
The female lays her eggs on the underside of the Turtlehead leaf
The eggs are yellow or orange and are laid in a large cluster
Essentially, Baltimore Checkerspot Butterflies are tent caterpillars. Oh no! Not dreaded tent caterpillars. Unlike the Eastern Tent Caterpillars and the Forest Tent Caterpillars, the checkerspots do not defoliate forests. They make their tents around their perennial foodplants and have no reason to ascend into the trees.
The silk tent is woven around the Turtlehead plants
The early instar of the Baltimore larvae create the tent
Unlike most butterfly species that deposit their eggs individually on their host plants, Checkerspots lay large clusters of eggs on a single leaf. The young caterpillars feed together and collectively spin a large silk tent around the host plant. The tent offers them some degree of protection from predators - at least during the early period of their development. Ichneumon wasps patrol the outside of the tent and search for outliers that they can reach with their ovipositors and attempt to parasitize. When does a checkerspot  caterpillar appear to metamorphosize into a wasp? That's after its had an ichneumon egg laid inside of it.
These caterpillars are now large enough to live outside of the tent
The Baltimore caterpillar starts to shed its final larval skin
Later instars of the checkerspot caterpillars are more independent and they feed without the protection of the tent. Their larval skins are covered with hairs which make them  unpalatable to most birds and other predators. Baltimore chrysalises are small structures, but they are colorful and well bejeweled. Certainly it's a fitting packaging for one of our gaudiest butterflies.
The ornate chrysalis of the Baltimore Checkerspot
I was watching several Checkerspots as they raced around the meadow. Males were chasing off other males while females were scouting for their host plants. Some females had noticeably swollen abdomens and were presumably full of eggs, but the one that I followed appeared to be empty. She kept landing on turtlehead leaves, but although she went through the motions of laying, nothing was being deposited on the leaves.
Note the orange antenna clubs, eyes and legs
An explosion of orange - the Baltimore nectars on Butterflyweed
Nectaring on Valrian flowers
The males were mostly nectaring on Valerian plants. These tall non-native perennials superficially resemble wild carrots and parsnips, but unlike those common plants, Valarian is not in the parsley family. The plant has been expanding primarily in damp meadow habitat throughout the region. A decade ago we had only a few patches of it, now it is difficult to find a place where they are not represented.    

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