Saturday, February 21, 2015

An everyday epiphyte

Mistletoe, Phoradendron spp.
Great Purple Hairstreak
Remember this guy (at left)? Remember how his caterpillars only eat mistletoe? For this and other reasons, our Texas mistletoe (Phoradendron spp.) is worth another look.  Mistletoe is an arboreal hemiparasite, related to sandalwood (another hemiparasite), with fleshy green leaves and stalks. It grows best as a rounded clump in the upper branches of hardwood trees where it has access to abundant sunlight and can practice its nutritional thievery unmolested.

Besides the caterpillars of the lovely great purple hairstreak and some other Lepidoptera, few creatures eat the toxic leaves of this plant. Birds, however, adore its fruit.  The berries are a valuable winter food source. Providing winter nourishment is not an act of philanthropy on the part of the mistletoe. Mistletoe berries are extremely sticky. Birds eat and poop them out, wiping off their little tails, feet, and beaks on the branches of a preferred roost, effectively dispersing the mistletoe progeny. It's ingenious. Humans appreciate and disperse mistletoe berries for their own purposes. Specifically-- stolen kisses in the holiday season.
A few white berries

Despite its bad reputation, mistletoe is unlikely to bring down a tree single-handedly. It may sap the vigor and weigh down individual branches, but it is unlikely to seriously harm an otherwise healthy tree. This is good news, because once established mistletoe is nigh impossible to remove. Cutting off a branch to excise the plant causes more harm to the host tree than leaving it in place. This practice is unlikely to completely remove the mistletoe anyway.

By flowering and fruiting in the winter, mistletoe provides resources when little else is available. It is well past time for blooming, but I saw some mistletoe flowering today anyway. The inconspicuous yellow flowers are a pollen source during this season of scarcity. Male and female flowers occur on different plants, and reproductive development is slow. Mistletoe doesn't typically flower before its third year. The large clusters you see in treetops are decades old.

I like epiphytes and parasitic plants.  I don't really have a good reason-- I guess they have a "tropical" feel. I can understand a homeowner not being thrilled at the arrival of this clever little plant on a favored shade tree, but seeing as there's no stopping it, you may as well take a philosophical perspective.  You can decide to appreciate its genius, and be comforted that it is unlikely to do serious harm for a few more decades.
Male flowers?

Monday, February 16, 2015

Spring heralded on valentine's day at Tandy Hills

A honey bee enjoys her non-traditional flowers on Valentine's day
We had perfect weather for a walk on Valentine's day this year, so I decided to tool around Tandy Hills and see how spring is progressing in this part of the metroplex. More butterflies were out. I saw little yellows and possibly dainty sulphurs, in addition to the occasional question mark canvassing about in the sunshine. I know question marks over winter as adults, but I didn't expect the appearance of the little yellows. Apparently they also overwinter as adults in the southern part of their range.

Blooming vetch?
These butterflies weren't nectaring, but they were actively flying on the ridge top. I didn't notice many green legumes for their caterpillars to eat, so I wonder if what I saw were males patrolling for females. In many butterflies and moths, the males emerge first in the season. They use their head start to stake out females.

I also saw a few honey bees out scouting for food. Other than dandelions, hen bit, and the occasional vetch, there wasn't much available. The honey bees seemed to ignore these flowers in favor of the small yellow elbow bush blossoms (Forestiera pubescens). Elbow bush is one of the first shrubs to bloom in Texas. It's flowers tend to appear in February or March, so it's right on time this year. Other common names for this plant include "spring herald" and "stretch berry".

It is fortunate that these honey bees have a few flowers from which to chose. Flowers like dandelions are deficient in multiple amino acids which honey bees are unable to manufacture. The bees would effectively starve and be unable to rear brood if that was the only pollen available.  By collecting pollen from multiple sources, they ensure that their diet satisfies the colony's nutritional requirements.

Busy loading up her saddle bags with food for the hive

Sunday, February 8, 2015

Emergence and old skins

Shed snake skin
I was out looking for the first signs of spring at Fort Worth Nature Center yesterday. Trout lilies and other spring ephemerals emerge about this time of year in Texas, and spring itself will be truly upon us in another month. The birds were chattering and excited. I only realized I had missed them upon hearing them call again.

Question mark butterfly
I jumped the gun a little on wildflowers, however. It's still a bit early for them, despite the taste of perfect weather we've had this week. I did see other signs of the new season. A neatly coiled snakeskin sat on top of crispy brown leaves. Its perfect placement made me think it hadn't been there all winter. I don't know when snakes normally emerge from hibernation in Texas, but February seems premature.

Question mark butterflies were also awake and flying in the sun. These butterflies overwinter as adults. They roost in crevasses in tree bark, but they break dormancy on warm days. I didn't see much for them to feed on, but they seemed compelled to flit about. I don't imagine that butterflies 'play', that's what it looked like they were doing.

I also found an empty silk moth cocoon dangling from a small shrub. I'm on the fence as to whether the cocoon is from this year or last. It is remarkably well preserved, and it is certainly well attached to its little twiglet, but in our region silk moths don't normally begin to emerge until March.

Native silk moths are enormous, fuzzy, and brightly marked. The sea green luna moth is one of the more familiar representatives. Silk moths have an outer silk cocoon protecting their pupa. The silk moth used for commercial silk production is the only fully domesticated lepidopteran. They don't exist in the wild.

Adult silk moths do not have mouths. They do not feed as adults- they live for a week or two and are entirely consumed by the need to breed. In fact, some moth watchers rear female moths in order to use their pheromones as bait to lure in males of the species.

A luna moth- a type of silk moth
Until yesterday I'd never wondered how these mouthless moths fight their way out of their cocoons without mandibles. Apparently they either split their cocoons with a built-in escape hatch that only works from the inside, or they exude silk dissolving chemicals ("cocoon-ase") to ease their emergence.

Snakes and silk moths are both taken as symbols of rebirth and renewal, so it is fitting that I found them while out looking for signs of the changing season. As for spring beauties and trout lilies, I'll just have to keep checking. I don't mind the task.

A closer view of the cocoon