Friday, April 27, 2012

News from the Dark Red-tail Female

Last year we happened upon a red-tailed hawk nest in a Saguaro not far from our house. Two nearly grown chicks were raised by a female on her own. At least we never saw a male around. But the chicks were so big then that we hoped that they all made it.

In February of 2012, last year's nest was not in use. But close by, an even older nest, also in a saguaro, was being renovated. To our dismay the birds used a huge black plastic bag for decor. It worried me how it would withstand our fierce winds or whether it would suffocate the nestlings when it got really hot...

By mid-March, the dark female was sitting on eggs and she never seemed to move from the nest - we kept our distance. Around her, the plastic bag was rattling in the wind, but it was being shredded by the cactus thorns.

 When we came back in early April, the female was sitting in an Ironwood tree close to the nest, and her warning call brought the male from his distant hunting ground. He is very light colored. Together, they told us that we weren't wanted.

 In the rough cluster of creosote branches that constitute the nest, a little white downy bump was visible. The head of at least one small chick.

The little white spot is hard to see, but it moved, and very shortly, there was a second one to the right of it. 

 This morning, more than two weeks later, we went back, were screamed at again, and got a short view of at least two rather large but still downy chicks. They were hunkering down in the nest, but did keep a wary eye on us. So we quickly left. I hope that next time we visit we will find them already standing up and loosing their downy baby fluff.

Thursday, April 19, 2012

Cutworms are beautiful

In fact, I am absolutely smitten with their velvety texture and beautiful, delicate patterns in soft earth tones highlighted with metallic accents.

 It didn't start that way. In early spring, when I turned rocks or dead wood around our house, instead of the interesting  tenebrionid beetles I was looking for I found fat, hairless brown caterpillars. They were everywhere, even under dry cow pies. They were so indistinct that I got no reaction when I posted one on Bugguide and it took Eric Eaton's blog on cutworms to make me realize what they were. I learned that they do not feed on dead wood, fungus or dry cow dung, they just hide under it during the day. At night they go out  to chomp off young plants at the base, hence the name.

Euxoa auxiliaris

This year, our winter rains made the desert annuals sprout, so lots of caterpillars had food to develop into adults. My first cutworm moth of the season  had crawled behind one of my paintings on display at an out-door art show. As it darted out (Dart is the other name mostly applied to the adult moths) my customer backed off in disgust. After the show, another moth, or maybe the same art loving creature, got itself loaded into my van, woke up at night during the drive home and fluttered into my face. At least it kept me from falling asleep on Interstate 10.

Heliolonche carolus and Schinia miniana

 Then Dave Wagner, author of several books on eastern moths, visited and got me to look more closely at some day active Owlets, very pretty and in the same family as the cutworms.

Striacosta albicosta,  Euxoa serricornis,   Abagrotis reedi, Anarta trifolii 

When it got warmer I began running black lights at night again.
I have two lights, one in our driveway and one at our neighbors' house across the street. Both places have sandy soil, lots of Creosote, Saguaros, Palo Verdes, Ironwood Trees and a few Mesquites. The annuals are mostly Fiddle Neck Amsinckia intermedia, Scorpion Weed Phacelia, Bajada Lupine Lupinus concinnus, Filaree Erodium cicutarium, Evening Prim rose Oenothera primiveris, a small mustard and a small very common Cryphantha species. This relatively limited number of food plants supports an amazingly divers population of cutworms.

Only the last one in this row is identified so far: Anarte mutata
Including the ones that still need identification I count at least 12 to 15 different morpho-species that appeared since the beginning of March. It seems that every night brings new ones. The two lights, about 400 yards apart, show surprisingly different results, maybe because one is closer to a (dry) wash.

Lacinipolia sp.
These pretty lichen-patterned ones for example only come to the light at our house. Most identifications are  by Maury J. Heiman. Thank you so much, Maury!

Cutworm or Dart moths form the subfamily Noctuinae in the huge family of the Noctuidae, the Owlet Moths.

From my own observations I'm pretty sure that cut worm moth populations here in the desert sharply increase in years with winter rains and resulting spring flower emergence. I can very well imagine how constant irrigation and spring seeding of crops offer ideal conditions for high Cutworm populations in agricultural settings. Under those conditions some species in this group can become economically important pests.

Monday, April 16, 2012

Master Blister Beetle Procession

Walking with our dogs along the Santa Cruz River in Cortaro, we found dozens of 1 1/2 inch beetles crossing the road. All of them seemed to be determined to reach some unknown better place. They were Master Blister Beetles, Lytta magister.

Even mating pairs were on the move even though the females had to walk backwards. So the goal probably wasn't some super attractive pheromone source ... but then what?

Then again, the beetles probably asked a the same question watching the procession of human bikers, joggers, hikers, and even multi-species groups pass them ...Some beetles were definitely trying to get a better look

Thursday, April 12, 2012

Backyard Ant Hills

Mounds of the Leaf-cutter Ant, Acromyrmex versicolor, left and right.  Middle: Smooth Harvester Ant Messor pergandei
In our backyard, numerous colonies of ants build structures that look like mini volcanoes: cone shaped mounds that rise out of the sandy soil complete with central craters. At first steep and well-shaped, they soon get flattened by erosion. Some sit alone, others in groups of two or three. In spring, there is always activity around those mounds: workers carrying material into the entrance and disappearing with it in the dark depth, or dropping their loads on the outside of the mound, forming a ring of plant material around it.

I must admit that I lived surrounded by those ants for years before it dawned on me that there were two very different species at work and the differences are quite apparent.

At one type of colonies, the single minded efforts of a never ending procession of ants result in an accumulation of fresh green, purple or silver plant clippings that sit there for a day and then disappear into the crater (top right). These are the leaf-cutter ants that I will describe in a later blog.

The plant material circling the other type of colonies looks old and discarded. The ring around the mound seems to be the permanent waste midden of the colony (above, middle).
 This is the work of the Smooth Harvester Ant Messor pergandei. In this and the following blog I will not describe the social structure of ant communities that both species have in common, but rather point out the most striking differences in the way of life in these two local crater-building species...

Messor pergandei, the Smooth Harvester Ant
 Messor pergandei ants are shiny, dark brown to black, the majority (workers) between 4 and 8 mm long. Their mounds are of modest height and usually around 20 to 30 cm wide. I find them in open, sandy areas, often along paths - there doesn't seem to be any particular requirement for shade or moisture and these ants can deal with very compacted soil.  The common name Harvester Ants refers to their striking behavior: workers are constantly carrying bits and pieces of plants to the mound, and they are choosing their material in a very organized way, clipping the heads of grasses when the seeds are fresh and juicy, switching to other seeds when those are in season....

Erodium cicutarium, Redstem Filaree
 In our desert surroundings a little plant in the Geranium family, Erodium cicutarium, also known as Redstem filaree, or Common Stork's-bill, is very common. It is an introduced, invasive Mediterranean species. Messor ants don't care. In early March, they prefer Filaree seeds over anything else. Filaree relies on ants for seed dispersal  (myrmecochory). As an incentive for the ants, a piece of sweet tissue (elaiosome) is firmly attached to each seed. The ants collect the diaspores (seeds plus elaiosomes) and carry them to their nests.

Workers were bringing seeds with their spiraled attachments from all over and carriwd them into the dark entrance hole of the colony. Other pieces that were brought up from the inside and then tossed over the crater's rim to end up on the colony midden. These are just the inedible parts, which include the intact seed. The sweet elaiosomes have been removed and  remain in the under-ground granaries of the colony.  

Messor ants like Erodium diaspores so much that most middens that I checked in March 2012 consisted of nothing else. This raises the question whether seed dispersal is actually achieved. While the seeds are removed from the mother plant, they still end up in dense piles, exposed to elements and rodents. If this is a glitch in the system, it's probably because Erodium and Messa really didn't co-evolve. I would like to observe the behavior of local ants in the Mediterranean home countries of the plant. But, alas, when I studied insects in Yugoslavia, Greece, and Italy, ants were not very high on my list. However, if the spread of Erodium in our backyard and the adjoining state land is any indication, it's a successful symbiosis, even here in Arizona.

Veromessor pergandei refuse heap in October after a good monsoon: hulls of cheat grass seeds are rejected and piled around the nest entrance
The big colonies of Messor pergandei are very active right now. The ants become nearly invisible during our 'dry heat; times from May to the beginning of July when the first monsoon storms trigger the mating flights of thousands of winged males following the young aleate queens on their bridal flight. The emergence of so many insect often looks like rising smoke. That is the time when suddenly hundreds of dragonflies hunt over the dry desert and bats dance over our house at dusk.
Messor pergandaei queen
Last year one of the queens shed her wings and wandered into my studio. When she was identified as a Harvester Ant I was apprehensive: my only experience had been with our other Harvester Ants in the genus 
 Pogonomyrmex, and that was the most painful insect encounter I can remember (and I have been attacked by fireants in Florida)

Pogonomyrmex sp. nest and worker
 But there is no Pogonomyrmex colony close to our house.  Local Pogonomyrmex nests look like nothing else: a more or less bare spot of several square yards with paths radiating away from an entrance hole somewhere off-center. I push my pant legs into my socks when I'm around these places. Messor ants on the other hand are so unagressive that I don't even know whether they can sting even though I have been on hands and knees with my video camera at their nest sites quite often.

P.s. the Genus name Messor has been changed to Veromessor for the US species since I wrote this entry