Formica obscuripes
| Formica obscuripes | ||||||||||
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Formica obscuripes , worker of the great morph |
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| Scientific name | ||||||||||
| Formica obscuripes | ||||||||||
| Forel , 1886 |
Formica obscuripes is arelatively large ant species nativeto parts of North America. It belongs to the genus forest ants ( Formica ) in the subfamily of scale ants (Formicinae).
features
The elongated eggs are about 0.6 millimeters long and 0.3 millimeters in diameter. The legless, white larvae reach a length of 6 millimeters. The pupae of the workers are 3.5 to 7 millimeters in length, while those of the queens and males reach 9 millimeters in length.
The workers exist in two, possibly three morphs of different sizes. The tall workers have a body length of 6 millimeters or more. Her head and thorax are orange-red, the abdomen black. Since they are primarily responsible for the transport of honeydew between the secondary and primary nests, they have a larger “ social stomach ”. The small and medium morphs are black overall.
distribution and habitat
The range of Formica obscuripes stretches from northern Indiana and Michigan in the east over southern Canada and the northern United States to British Columbia and Oregon . To the south, it stretches across Utah , Colorado and northern New Mexico to California . In this area, the nests are built in different habitat types, light pine forests , grasslands and steppes , which are characterized by stocks of sagebrush and other species of the Artemisia genus .
Nest building
The hill nests with scattered domes are covered with small, dry pieces of plants. The material that is abundantly available in the respective habitat is used, such as pine needles and twigs in pine forests, or stems of sagebrush or blades of grass in steppes or on grassland. The hilly nests are often surrounded by a ring of bare sandy soil. The volume of the hill nests can vary greatly depending on the age of a colony and the inhabited habitat. Typical is a height of half a meter above the ground and a diameter of one to one and a half meters. The breeding chamber usually reaches a depth of one meter or more, while the covering litter layer is thirty centimeters or less thick. It is characteristic of Formica obscuripes that slightly excavated, partially covered and almost straight ant passages lead from the hill nest to the nearby feeding grounds in trees or other plants. Formica obscuripes is considered a useful insect because of the loosening and mixing of the soil. It also eats various forest pests , including the economically important Western Spruce Budworm ( Choristoneura freemani ).
It appears that the Formica obscuripes colonies must keep a minimum distance from one another. If it falls below this or if the location of a hilltop is no longer suitable for other reasons, they will be relocated. The building materials and all the ants in a nest mound are brought to the new sand site via a single wide ant road. In one documented case, this process was completed after two weeks.
Way of life
The life cycle of Formica obscuripes includes a complete metamorphosis ( holometabolism ), from the egg to the larva and pupa to the imago . In the ant nest, the brood care and the care of the queens is taken over by the small and medium-sized morphs of the workers, whereby the small workers are largely restricted to the main nest. The large morph is engaged in the procurement and transport of food and in the construction and maintenance of the nests. If necessary, however, all activities in the colony can be carried out by all workers.
During the cold months of the year, the adult ants retreat to the underground area of the nest to overwinter.
Reproduction
In addition to the up to 35,000 or 40,000 adult workers, few female and male ants live in the colonies. The number of queens in a colony can vary, usually two or more. They live for several years and after their death the colony they founded perishes within a few months. Between May and August each year, depending on the climate, winged queens and males appear on the hill nests.
As part of an 18-year long-term study in a nature reserve in Michigan , Mary Talbot of the University of Michigan examined the reproductive behavior of several colonies of Formica obscuripes . During this period, flights were observed on 69 days, consistently with the first excursion at the beginning of June and in one case with the last excursion on July 1st. Flights did not take place in all years. The beginning and end of flight times and the number of flights from colony to colony varied considerably. In general, excursions to colonies in the shade of trees and on western slopes started later and with fewer flying days than in colonies on eastern slopes. The first winged ants appeared on the hill nests at around 17 ° C. Between 19 and 22 ° C they climbed grasses and the excursions started from a temperature of 20.5 ° C. The maximum flight activity took place at temperatures between 23 and 24.5 ° C, at over 27 ° C the flights were stopped. During the flight period, excursions took place on all days, provided there were still winged animals in the hilltop and rain, strong wind or an overcast sky prevented the excursions.
The ants from several colonies that had flown out found themselves together as a swarm within a few minutes of take-off on an almost stationary area of 15 × 15 to 35 × 45 meters, where the mating took place. The queens sought out slightly elevated locations on grass and other low-growing plants, while the males flew around at low altitudes between the plants looking for queens willing to mate. It happened that only males or only queens flew out of a colony. Most of the time, however, the number of males was far greater than that of queens, and only rarely were many more queens than males swarmed out. In these cases there was hardly any flight activity on the swarm area, as the males mated without ceasing.
The males die shortly after the wedding flight. The fertilized queens look for a suitable place to start a new colony and break off their wings. Unfertilized eggs develop into males, while fertilized females emerge. Whether a worker or a queen develops seems to depend on the nutrition of the larvae.
food
Formica obscuripes feeds primarily on honeydew , which the small and medium-sized workers gain as a product of excretion from various Schnabelkerfen (Hemiptera). Suppliers mainly include aphids (Aphidina), scale insects (Coccoidea) and humpback chirps (Membracidae) on trees and other vegetation near the ant nest. The transport of the honeydew from the harvesting sites to the primary nests, sometimes with secondary nests as intermediate stations, is usually carried out by the large workers. Small female workers are only occasionally seen transporting honeydew between the harvesting sites and secondary nests.
For the honeydew-producing insects, the ants offer a certain protection from predators and food competitors, for this reason their number is significantly larger on branches with Formica obscuripes . In addition, the host plants benefit from less damage caused by feeding on the branches populated by Formica obscuripes and their honeydew suppliers. The diversity of insect species that curl up leaves and use them as shelter is significantly greater on branches with Formica obscuripes .
In addition to the honeydew, the nectar of the late blooming bird cherry is a source of food during the flowering period . Formica obscuripes is attracted to the nectar available for several weeks after flowering. At this time there are also young butterflies of the species Malacosoma americanum on the plants , which are overwhelmed and consumed. Insects of other species and other arthropods form another component of the diet . Some of them are pests, so that the relationships between Formica obscuripes and the aphids and other honeydew suppliers, as well as their host plants and nectar suppliers , can be viewed as a mutualistic system.
Defense and procurement of building materials
Like other scale ants, Formica obscuripes can release a jet of formic acid from the end of the abdomen for defense . It has been observed that workers of plants in the vicinity of the nests peel off the bark at the base and inject formic acid into the cambium ring . This seems to lead to the death of the plants, which then dry up, disintegrate and are used by the ants as building material to expand the dome of their nests.
Ant guests
As a widespread species that dominates the ant fauna in some places, Formica obscuripes is the host of a large number of ant guests . They include at least two species of ant crickets of the genus Myrmecophilus , Myrmecophilus manni and Myrmecophilus nebrascensis . The relationship between Formica obscuripes and the 2.3 to 4.0 millimeter long Myrmecophilus manni has been studied in more detail in colonies in southeast Washington state. The range of the species stretches from Washington and Idaho in the north to Mexico and it has been found in the nests of at least thirteen different ant species. In the study area was Formica obscuripes the main host, more than half of the nest hill at the myrmecophilus manni was settled. The number of crickets in a colony ranged from 15 to 300. The crickets that live in the hill nests of the ants are generally attacked by the workers and only escape through their constant readiness to flee and their quick reactions. By imitating the ants' exchange of information by means of antenna crosses , Myrmecophilus manni succeeds in motivating the workers to participate in trophallaxis and to be supplied with food. They also often feel the ants' bodies to pick up food particles or the smell of the hosts. The 1.1 millimeter long eggs of Myrmecophilus manni are very similar to those of Formica obscuripes . In mid-July, the crickets hatch simultaneously in all ant colonies, even if the nest mounds are miles apart. The date of oviposition is probably determined by the photoperiod , while the duration of development is determined by the temperature in the nest mounds. For the spread from one nest mound to the next and between the colonies, the ant crickets use the ant trails that often cross each other.
Formica obscuripes is the host of several non-species-specific hover flies (Syrphidae) of the genus Microdon , Microdon albicomatus , Microdon cothurnatus and Microdon xanthopilis . For Microdon xanthopilis it is the type host and the most common host in Washington State. The adult hoverflies are active in the northern United States from May to June, rarely longer, and the females lay their eggs in the ants' nest mounds after mating. In their external appearance, the larvae of the flies resemble slugs or scale insects and have been repeatedly described as such by biologists. The newly hatched larvae move deep down into the ant nest, to the dividing line between the litter layer and the ground or a little lower. There they shed their skin several times and overwinter as the third larval stage. In the following spring, they migrate back up and pupate near the surface. The molt to the imago takes place at night in order to avoid attacks by the workers. With only one generation per year, a large number of comparatively small eggs, a long development from egg to larva and several hosts, the species mentioned follow the same reproductive strategy. It is not known whether, like some other species in the Microdon genus, they parasitically feed on ant larvae or other organic matter.
Several species of ants also live in the nest mounds of Formica obscuripes . For Formicoxenus diversipilosus with Formica hemorrhoidal just another host known without their hosts colonies of this kind are not viable. Of the individuals of this species, only the winged males and females leave the host's nest to mate. Leptothorax muscorum has a broader host range, its colonies can survive without a host colony, and the species occasionally lives in the same colony of Formica obscuripes with Formicoxenus diversipilosus . Adult Formicoxenus and Leptothorax move freely throughout the nest. Winged males and females are mostly found near the surface, while workers and queens live in deeper areas of the nest mound. There they set up their own partial colonies and brood chambers distributed over the host's nest in clumps of twigs and roots or in hollowed-out branches. They choose areas that are not visited by Formica obscuripes . The host ants ignore the guests or only treat them with slight aggression if the nest has been disturbed by an external cause. If an ant of the species Formicoxenus diversipilosus encounters one of the significantly larger hosts, it immediately stops and presses itself to the ground. The host ant touches it briefly and then continues on its way. It happens that an individual of Formicoxenus diversipilosus squeezes between two Formica obscuripes during trophallaxis and participates in the food exchange. The species is also capable of feeding on its own. It is possible that certain nutrients are obtained from the hosts that cannot be procured themselves because of the hidden way of life deep in the foreign nest mound.
Web links
- Formica obscuripes on AntWiki, with pictures and extensive bibliography (in English)
Individual evidence
- ↑ a b c d e f g h i j k l Mark Headings: Western Thatching Ant, Formica obscuripes (Forel) (Hymenoptera: Formicidae) . In: John L. Capinera (Ed.): Encyclopedia of Entomology . 2nd Edition. tape 4 . Springer Science + Business Media, Dordrecht 2008, ISBN 978-1-4020-6242-1 , p. 4214-4216 , doi : 10.1007 / 978-1-4020-6359-6_2648 .
- ↑ Michael W. Heikkinen: Negative effects of the western thatching ant (Formica obscuripes) on spiders (Araneae) inhabiting big sagebrush (Artemisia tridentata) . In: Great Basin Naturalist . tape 59 , no. 4 , 1999, p. 380–383 ( byu.edu [PDF; 1.3 MB ]).
- ^ A b Gregg Henderson, Roger D. Akre: Biology of the Myrmecophilous Cricket, Myrmecophila manni (Orthoptera: Gryllidae) . In: Journal of the Kansas Entomological Society . tape 59 , no. 3 , 1986, pp. 454-467 , JSTOR : 25084806 .
- ^ A b Mary Talbot: Flights and Swarms of the Ant Formica obscuripes Forel . In: Journal of the Kansas Entomological Society . tape 45 , no. 2 , 1972, p. 254-258 , JSTOR : 25082492 .
- ↑ Gregory M. Crutsinger, Nathan J. Sanders: Aphid-tending Ants Affect Secondary Users in Leaf Shelters and Rates of Herbivory on Salix hookeriana in a Coastal Dune Habitat . In: The American Midland Naturalist . tape 154 , no. 2 , 2005, p. 296-304 , doi : 10.1674 / 0003-0031 (2005) 154 [0296: AAASUI] 2.0.CO; 2 ( natesanders.org [PDF; 76 kB ]).
- ^ Roger D. Akre, G. Alpert, T. Alpert: Life Cycle and Behavior of Microdon cothurnatus in Washington (Diptera: Syrphidae) . In: Journal of the Kansas Entomological Society . tape 46 , no. 3 , 1973, p. 327-338 , JSTOR : 25082580 (work relates to Microdon xanthopilis ).
- ^ F. Christian Thompson: Revisionary notes on Nearctic Microdon flies (Diptera: Syrphidae) . In: Proceedings of the Entomological Society of Washington . tape 83 , no. 4 , 1981, p. 725–758 ( si.edu [PDF; 1.1 MB ]).
- ↑ RM Duffield: Biology of Microdon fuscipennis (Diptera: Syrphidae) with interpretations of the reproductive strategies of Microdon species found North of Mexico . In: Proceedings of the Entomological Society of Washington . tape 83 , no. 4 , 1981, p. 716–724 ( si.edu [PDF; 131 kB ]).
- ^ Gary D. Alpert, Roger D. Akre: Distribution, Abundance, and Behavior of the Inquiline Ant Leptothorax diversipilosus . In: Annals of the Entomological Society of America . tape 66 , no. 4 , 1973, p. 753-760 , doi : 10.1093 / aesa / 66.4.753 .
- ^ Philip S. Ward: A synoptic review of the ants of California (Hymenoptera: Formicidae) . In: Zootaxa . tape 936 , 2005, pp. 32-33 , doi : 10.11646 / zootaxa.936.1.1 .