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Brief Summary

    Phanaeus vindex: Brief Summary
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    Phanaeus vindex, the rainbow scarab or rainbow scarab beetle is a North American dung beetle, with a range from the eastern US to the Rocky Mountains. The head is a metallic yellow color, and males have a black horn which curves backward toward the thorax. Both sexes have yellow antennae which can retract into a ball on the underside of the head. The thorax is a shiny coppery color, with yellow or green on the sides. The abdomen is metallic green. The underbelly is black and green. Body length is about 2–3 cm (0.8-1.2 in) long.

    Males and females work in pairs to dig burrows beneath animal excrement. They move some of the excrement down into the tunnel, where the female lays her eggs in it. The grubs feed on the excrement for several instars until pupating.

    This species, like all dung beetles, are not pests, and play an important role in reducing fecal matter in the environment, thus reducing the number of disease spreading flies.

Comprehensive Description

Distribution

    Geographic Range Distribution
    provided by EOL authors

    Phanaeus vindex is native to the United States, from Massachusetts to South Dakota in the north, and Texas to Florida in the south. They are present in every part of Florida except the Florida Keys and the Everglades (Woodruff, 1973), and in every area of Texas except a huge triangular region in south and central Texas. Their existence is limited to north of Mexico near the east of the Atlantic Ocean. They also occur in New Mexico in the west (Bertone et al., 2004). In Western Oklahoma, they are completely absent due to the presence of P. difformis (Blume and Aga, 1978). All P. vindex are typically sighted from spring to autumn (Bertone et al., 2004).

Morphology

    Morphology
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    Phanaeus vindex beetles (Rainbow scarab) are bright metallic green, blue, and red with gold reflected (Woodruff, 1973) off of their compressed heads (Bection, 1930). Males also have a horn on their head, some smaller than others (Woodruff, 1973). Male horn size is usually dependent upon nutritional status in their larval stage (Bertone et al., 2004). Their colors may be used for mating signals (brightly colored males may be more attractive to females) (Vulinec, 1997). Male horns also reflect UV light so the light and colors reflected off of their horn may serve as a warning to predators (Vulinec, 1997). P. vindex have an alimentary tract that is about eight times their body size with 3 divisions: the esophagus, the stomach, and the hind-intestine (Bection, 1930). Their stomachs make up about 7% of their body size and rest between the wing muscles. In males, the thorax raised is above the elytra to protect their back wings. Males lack a front tarsus (Woodruff, 1973). Females do not have a raised thorax (Woodruff, 1973), most likely because they experience less competition. Adults range from 1- 2.2 cm long in size (Woodruff, 1973). Both male and female have antennae (Woodruff, 1973). Their mouths are well-adapted for dung-eating in several ways. They have a mouth that is 1/3 the length of their head and they have furry and flexible rounded cutting edges in their mandibles for the consumption of soft, mushy feces (Miller, 1961). Larvae generally have a C-shaped body structure and a hard head with a soft body (Woodruff, 1973).

Habitat

    Habitat
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    P. vindex occur throughout a huge range of areas including grasslands, deserts, forests and semidesert places (Edmonds, 1994). They build burrows which are holes dug and used to save food, protect offspring and protect adults from parasites where they spend the majority of their time (Blume and Aga, 1978). Although P. vindex prefer grasslands, they have a high tolerance for various soil types and they utilize sandy soils or clay soils most often when they coexist with other species of the same genus (Blume and Aga, 1978). For example, when in the vicinity of other species such as P. difformis, they become constrained to clay soils such as in southeast Texas (Blume and Aga, 1978). Sandy soils have been noted to result in desiccation of larvae (Bertone et al., 2006).

Associations

    Associations
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    Beetles that are able to detect dung easily are favored by selection (Price and May, 2009). P. vindex beetles eat animal dung with a preference for swine and human dung, though they are also regularly found on cattle dung (Blume and Aga, 1978). They are also typically fast fliers (Price and May, 2009). In contrast to most scarab beetles, which fly fast until they detect food by its odor they land directly on the feces (Price and May, 2009), P. vindex lands about 1 meter from the dung then walks toward it (Price and May, 2009). They use sunlight, stars, and the moon for orientation in order to walk in straight path (Dacke et al., 2013). P. vindex also often move their food a few meters away from its original location in order to prevent other individuals from stealing it (Price and May, 2009).

    Phanaeus vindex are classified as “ecosystem engineers,” (Boze and Moore, 2014), because they improve the grasslands used for the feeding of cattle by decomposing cattle feces (Bertone et al., 2004). They are also essential in enriching the soil by increasing nutrient cycling (Bertone et al., 2006) and can reduce disease transmission from flies by reducing feces in the environment (Boze and Moore, 2014). When in a laboratory setting, these beetles are easy to manage because they can consume fruits such as banana, and are easily collected (McCann et al., 2008).

    Predation
    provided by EOL authors

    Burrowing owls prey on P. vindex (Woodruff, 1973). Mites such as Macrocheles amygdaligera (Woodruff, 1973) are also a big threat to P. vindex. They are specialized to cling to the beetle and thus are dispersed from dung pat to dung pat (Woodruff, 1973).

    Studies find these beetles are more likely to be infected by Physocephalus sexalatus, a nematode, than any of the other beetle species (Fincher et al., 1979). Because they are very active throughout the day and are big and bulky, P. vindex are typically found and ingested by swine, and can serve as an intermediate host for nematodes (Blume and Aga, 1978).

    When they are not foraging, P. vindex spend most of their time in their burrows, positioning themselves at the entrance (Price and May, 2009). When they sense a predator by shadows or movement, they fall to the bottom (Price and May, 2009). In laboratories where they were given new food frequently, they remained in their burrows for months (Price and May, 2009).

Behavior

    Behavior
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    Females have a low fertility rate but reproduce more than once per lifetime (they are iteroparous) (Price and May, 2009). Females can burrow by themselves; in this case they build a hole beneath or close to where the dung is (Price and May, 2009). Many of them also create close relationships with both male and female beetles to perform joint digging and nesting before the females are able to reproduce, (Price and May, 2009). Outside of burrows there is high male to male competition over females (Price and May, 2009). Females prefer males that are willing to provision burrows (Price and May, 2009). A male benefits when he prevents other males from having access to a female until she lays his eggs because females will mate multiple times. Thus, P. vindex males will achieve higher fitness if they exhibit willingness to provision burrows because this increases the probability of offspring production (Price and May, 2009).

Life Cycle

    Life Cycle and Reproduction
    provided by EOL authors

    In the ideal situation, males collect an amount of dung to be inserted into a burrow by the female (Thomas, 2001), and both sexes use their head and front legs to do so (Price and May, 2009). After checking with their heads to see if the burrow is compacted tightly enough they will mate. If they determine that the burrow is not compact, both the male and female will leave to start a burrow somewhere else (Price and May, 2009). Each nesting site has one or more brood balls (Price and May, 2009). Brood balls consist of dung for food and soil for preservation (Bertone et al., 2004). Once the brood ball is complete, the male and female mate and the female lays her egg in the brood ball (Woodruff, 1973). Another burrow with a brood ball is then constructed for the newly emerging adult or larvae to feed on (Price and May, 2009). The male and female then cease to be caretakers of the egg, although they do stay in the burrow (Price and May, 2009). In dung beetles, after the egg hatches in approximately 1 week, it develops into a larva and then transitions to an adult (Thomas, 2001). Larvae typically pupate within 3 weeks (Thomas, 2001). Adult P. vindex come out of the brood ball due to rainfall or temperatures rising, mainly in spring (Blume and Aga, 1976). They are known to hibernate in the winter (Blume and Aga, 1976). Once they come out, dung beetles repeat the same cycle of finding a mate, provisioning a burrow, and reproducing (Price and May, 2001). Adult P. vindex can live over a year (Eaton and Kaufman, 2007). P. vindex are likely to live a smaller amount of time in the field than in a laboratory setting due to the fact that in the former, beetles have to leave their burrow frequently to seek fresh food, whereas in a laboratory setting, their food is being renewed by overseers, they are less likely to encounter predators, and to encounter competition over dung.

Reproduction

    Reproduction
    provided by EOL authors

    Information is limited on the reproductive biology of P. vindex (Blume and Aga, 1978). However, P. vindex are able to interbreed successfully with Phanaeus difformis, (Price, 2005), though the offspring have reduced fertility (Blume and Aga, 1978). Beetles that appear as intermediates of P. vindex and P. difformis have been sighted in eastern Texas.

Conservation Status

    Conservation
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    P. vindex are apparently secure throughout their range. Future research should continue to evaluate their prevalence across their range.

Threats

    Threats
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    Common threats to dung beetles such as P. vindex include paracitides such as abamectin, ivermectin, eprinomectin, and doramectin, which are likely to kill beetles that ingest the dung these chemicals were poured on (Bertone et al., 2006). Pyrethroids, a type of insecticides, can be poisonous to beetles that ingest the cattle dung the pyrethroid were poured on, causing infection to the beetles for a week after ingestion (Bertone et al., 2006). Infected beetles begin to exhibit anorexia by eating only half the amount of feces than they would normally (Boze and Moore, 2014). Infected beetles also bury less dung and bury it in holes that are less effective than normal (Boze and Moore, 2014).

Management

    Management
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    To reduce contact between P. vindex and pesticides, pesticides and parasiticides should be distributed to cattle orally (e.g., ivermectin which can be orally formulated) rather than pouring them on the ground where animal dung is exposed and/or where these beetles (Lumaret and Erroussi, 2002). Using pesticides that are less poisonous, such as moxidectin, is another good alternative to managing parasite and pest populations while protecting dung beetles (Bertone et al., 2006).

Benefits

    Relevance to humans
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    P. vindex is the intermediate host for stomach worms, such as nematodes, to enter the cells of swine that ingest dung beetles (Fincher et al., 1970). In terms of aesthetics, scarab beetles are used for jewelry and were worshipped by ancient Egyptians (Woodruff, 1973). Environmentally, dung beetles reduce the buildup of wastes, recycle nutrients, and improve soils by eating dung (Bertone et al., 2006). They also reduce the dispersal of parasites over the land’s surface by burying dung 1 m deep into the soil (Fincher and Stewart, 1979).