Ladybird Beetle

 

Common Name: Ladybird Beetle, Ladybug, Lady Beetle– The name dates to the Middle Ages as “the beetle of our Lady” in reference to the Virgin Mary. The more vernacular ladybug is an American idiomatic form that mistakes a bug (order Hemiptera) for a beetle (order Coleoptera).

Scientific Name: Coccinella novemnotata – The genus takes its name as the archetype of the lady bird family Coccinellidae. Both the genus and family are from the Latin word coccineus which means scarlet-colored (originally from the Greek word for berry, kokkinos. The species name is from the Latin novum meaning ‘nine’ and notatus meaning ‘mark.’ The nine markings are the black dots; there are four on each of the two elytra (the protective red covers over the folded wings) and one on the scutellum (the horny, shield shaped plate just behind the head). The descriptive species is a ‘scarlet-colored nine marks’ beetle.

Potpourri: The anathema accorded to most arthropods is absent in encounters with the colorful and predominantly benign ladybird beetle. On the contrary, it is adored to the point of reverence in its assignation as the beetle of the Virgin Mary, the scarlet elytra symbolizing her cloak. That this sentiment is pervasive is evidenced by its variety of names in other languages and cultures. The French refer to coccinellids as les bêtes à bon Dieu (animals of the goodness of God) or les vaches de la Vierge (cows of the Virgin Mary); in Germany they are Marienkäfer (Mary’s beetles); in Russian they are called божья коровка (God’s little cow). In History of the Ladybird by A. Exell, it was reported that there were 329 different names for the iconic beetle based on surveys in 55 countries; among these, 80 referred to the Virgin Mary and 50 referred to God. The seemingly arbitrary adulation of the ladybird beetle is neither a religious solecism nor a misplaced metaphor. The apotheosis of the beetle to a consort of deities is a measure of the appreciation of the largely agricultural societies of the Middle Ages in Europe for the ladybird’s voracious appetite for aphids and scale insects, the banes of the farmer as destroyers of crops. It is likely that the presence of the beetle would mean that a superior crop yield in the absence of insect damage, a result which would surely be worthy of a prayer of thanksgiving in an epoch characterized by cyclic starvation. The ladybird beetle instantiated goodness.

There are about 5,000 identified species in the ladybird beetle Family Coccinellidae distributed globally; roughly 500 are indigenous to North America. They are for the most part carnivorous in their consumption of aphids, scale insects (superfamily Coccoidea), mites, mealybugs and whiteflies, though there are a few herbivores (about six in the subfamily Epilachninae) that are a major pests for melon, potato and bean growers (notably the Mexican Bean Beetle, Epilachna varivestis). Their consumption of aphids is prodigious; an adult ladybird beetle can consume as many as 50 a day amounting to 5,000 over a nominal two year life span. Even the larvae are voracious predators (they look like small alligators), consuming over 300 aphids during the two week period during which they grow so fast that they molt four times – a skin-shedding sequence that is known as an instar – in preparation for pupation, a teneral period of several days, and finally, adulthood.

The beneficence of the ladybird beetle in the protection of food crops in Europe as manifest in its near deification has not been as effective in the much larger and more primitive nascent fields of North America. While likely unnecessary, the perceived need to protect the burgeoning farmlands of the Americas led to the introduction of the most common ladybird beetle from the English countryside, the seven-spotted C. septempunctata sometimes referred to as simply C-7 (the seven spots added to the symbolism of the red elytra for the cloak of Mary in signifying her seven joys and seven sorrows). Due to this importation, the C-7 has become the predominant species in many areas, having supplanted the indigenous nine-spotted C. novemnotata or C-9 (pictured above) that was originally one of the most common coccinellids in North America.

The importation of ladybird beetles in the protection of crops from insect predation has not without success, however; the most well-known introduction averted an agricultural disaster. In 1880, the citrus growers of California discovered an infestation of orange trees in the area south of San Francisco which came to be known as San Jose scale. Investigation by agricultural experts led to the identification of the culprit: cottony cushion scale (Icerya purchasi) which was traced to an agricultural shipment from either China or Australia (accounts differ). By the beginning of the 20th Century, the infestation had metastasized to the extent that the entire citrus industry of California was at risk of collapse. The U. S. Department of Agriculture was consulted for direction; C. V. Riley, the chief entomologist responded with the recommendation that predator insects should be considered, a fairly radical proposal that at the time was viewed with justifiable skepticism as it had never been done before. Nevertheless, he prevailed against the opprobrium, dispatching Albert Koebele to Australia to search for candidates, who identified two species that were observed to prey on the scale insects – an obscure fly and a ladybird beetle called the Vedalia Beetle (Rodolia cardinalis). Koebele collected several hundred beetles, and dispatched them to California where they were placed in an infested orange grove that was contained within a screened enclosure necessary to the limits on variability of scientific experiments. The results were momentous: the scale insects were exterminated in a matter of days. Subsequent expansion of the Vedalia Beetle to the citrus groves of California resulted in control of the cottony cushion scale in two years. The citrus industry was saved; the ladybird beetle earned the beatification and canonization implied by its European holy assignations.

The California citrus miracle demonstrated the efficacy of natural predation on insidious pests; its success precipitated the age of ladybird beetle importation to North America. According to Steven Marshall in Insects, Their Natural History and Diversity, a total of 179 coccinellids were introduced for purposes of pest control in the 20th Century of which 15 have established self-sustaining enclaves of the ecologically naturalized. The most well-known is the Multi-colored Asian Lady Beetle (Harmonia axyridis), identifiable by the characteristic white marking on the pronotum (the dorsal plate over the thorax), as seen the attached picture. It has proliferated to the extent that it is now considered a pest in much of eastern North America, primarily due to winter sheltering. Ladybird beetles overwinter as adults and have evolved to enter a hibernation-like state called diapause to reduce energy and therefore nutrient demands during the colder period. To mitigate the thermal gradient, they seek out warmer places, like the cement and brick crevices on the south side of buildings. Due perhaps to their Asiatic provenance, the H. axyridis are attracted to houses, penetrating the walls and collecting in piles in attics and beneath windows usually in large numbers – often in the thousands. Not very lady-like at all.

 

The problematic pullulation of ladybird beetles is a result of two primary factors, one relating to their prey and the other relating to their not being preyed upon. Aphids and scale insects, the primary food source of coccinellids, evolved with the evolutionary survival strategy of producing huge multitudes of offspring, providing a relatively abundant source of nutrition. To insure even greater survival in the event of the inevitable but infrequent scarcity of prey, female ladybird beetles produce infertile eggs as a supplement to those that are fertile – the former to provide food for the larval hatchlings of the latter. In extreme cases, ladybird beetles resort to cannibalism, the ultimate survival food. The overall result of multiple food sources is that relatively few starve, though probably some are eaten. However, the primary reason for the ubiquity of coccinellids is the fact that they have few if any natural predators. The body fluids of the beetle – called the hemolymph – contain alkaloid toxins (one of which is appropriately called coccinelline) that have a rebarbative smell and repellent taste. When disturbed, the beetles exude the yellowish hemolymph from their leg joints, providing an olfactory signal to deter potential predators and a taste that would limit a determined predator to only a few beetles. However, the mephitic smell and rancid taste are not the primary deterrents. The bright red coloration of the ladybird beetle is commonly associated with toxicity; the red eft stage of the red-spotted newt and the adult monarch butterfly are examples. Any potential predators are therefore visually forewarned and therefore likely dissuaded. The use of color to avoid predation is called aposematism. Since many ladybird beetles survive due to profligacy of prey and few are removed by predators, the potential exists for a great number of beetles to pass from one generation to the next – the makings of a pest. Marshall recounts an infestation in 2000 during which swarms of H. axyridis were observed doing things like “nipping people and damaging fruit.” The latter effect has had a deleterious effect on viniculture due to direct damage to grapevines. But the more nefarious problem to vintners is contamination of the harvested grapes with beetle carcasses; their noxious smell and taste contaminate the must – the resultant wine unpalatable.

The ladybird beetle is popular with children; its bright colors and aesthetic hemispherical shape evoke visions of fairy gardens and magic kingdoms of numinous origin. This infatuation is certainly reinforced by their adult guardians, who, as has already been established, deify the beetle. The popular nursery rhyme of English and American school children is pervasive:

Ladybird, Ladybird fly away home
Your house is on fire, Your children do roam
Except little Anne who sits in a pan
Weaving gold laces as fast as she can.

According to the Encyclopedia Britannica, an reasonable authority on British folklore, the nursery rhyme refers to the burning of the hop vines after the harvest. This was done to clear the fields for the next harvest with the unintentional side effect of killing the ladybirds that lived there to eat the aphids and scale insects. Supposedly, little Anne was the name given the ladybird larva and the weaving gold laces is a reference to molting. In that there are variations to the English plaintive in different languages, it is likely that the words were chosen nonsensically so as to provide simple rhymed words suitable for the primitive vocalization skills of children. The Russian version dispatches the ladybird beetle to heaven where her children have candies that they give away to others but not to their mother, not a particularly compelling morality.