How the firefly glows

Biolumination, the creation of light by living things, is an evolutionary strategy that has formed multiple times for different reasons. But in the case of the fireflies, or lightning bugs if you prefer (despite them not being members of the true bugs, but that was last post), the cause for all the ephemeral lights generally comes down to one thing, sex.

Members of the family Lampyridea, or as they are more commonly known, fireflies, are a group of beetles that have developed the ability to use light for communication. Being beetles, a good portion of their lives are spent underground as larvae feeding off of soft bodied invertebrates such as slugs, snails and earthworms. Even at the larval stage, the glowing abdomen can be found in some species if flipped on their back. In this instance, the firefly is taking use of a secondary purpose behind glowing known as an aposematic signal. This is a warning to all those who find it that, due to chemicals unrelated to illumination, the creature possesses a terrible taste. In this case, the use of light is quite similar to the bright colors of certain poisonous frogs.

The production of light, in both the larvae and the adults, occurs in the abdomen. Here, on the underside of the posterior abdominal segments, within specialized cells known as photocyes, a chemical reaction occurs that produces the light. In the case of fireflies (as there are many ways to produce light), they begin with a florescent substrate known as Luciferin. While Luciferin can produce some light when oxidized, fireflies use an enzyme known as Luciferase to speed up the reaction. While Luciferin on its own only produces one wavelength of light, changes to the shape of the Luciferase enzyme in different species allows for the production of the wavelengths of yellow, green and even red light.

The reactions use of oxygen is key to the fireflies control over its light. While the nervous system does not directly contact the photocytes, it does connect to nearby cells. When the firefly wants to light up, it sends a signal to these neighboring cells to start producing nitrous oxide which is then absorbed by the adjacent photocytes. The photocytes have arranged their mitochondria (the source of energy for a cell) along the outside so that oxygen is used up by them before it can react with the Luciferin produced within the cell. But once nitrous oxide starts to be absorbed, the mitochondria start to metabolize using this gas instead, allowing for oxygen to diffuse deeper into the cell where it can finally be used in the reaction to produce light. As long as the supportive cells produce nitrous oxide, enough oxygen will diffuse throughout the cells for the firefly to glow. But once the production of nitrous oxide stops, the mitochondria go back to using oxygen which interrupts the oxygen flow, preventing the light producing reaction. In this round about manner, the firefly can appear to flick on and off.

All of these complex pathways have evolved for the sake of sex. For when it comes to reproduction, evolution will take any and all possible paths it can so that the individual’s genes may be passed on. The flashing is used as a sign of fitness, the longer and brighter the flash, the better suited the mate. Many females, who often do not develop wings and may even stay in a permanent larval form, use their own light to signal to the males whether they are interested or not.

The color, frequency and duration of the flashes are unique to each species. This prevents an individual from trying to attract a mate only to find out that it is the wrong species. However, one genus has taken advantage of this distinction. Females of the genus Photuris will mimic the flashes of the females of members of a different genus, Photinus, to lure in incompatible males. Once lured in, the female Photuris will eat the unsuspecting male so that it might gain the toxins it produces. It seems Photuris has found a more efficient way of becoming inedible than just producing the chemicals herself.

Thank you JuneBug for the request!

Superfamily Pentatomoidea – The stink bugs

The insects known more commonly as the stink bugs, shield bugs or chest bugs are all members of the large superfamily Pentomoidea. There are approximently 7000 known species divided up amongst 14 to 15 families (depending on the system preferred by the consulted taxonomist). All are distinguishable by a similar body plan, the structure of their mouth parts and their varying use of chemical defenses.

Members of the true bugs (order Hemiptera), stink bugs are often mistakenly called beetles (order Coleoptera), despite having being members of a distinct order. While there are a number of anatomical differences between the true bugs and the beetles, one of the most distinctive can be seen in their mouth parts. Members of the true bugs all have modified their mouth parts into a sucking proboscis like structure. Composed of fused mandible and maxillae used for piercing and housed within a labium, most stink bugs use this proboscis to feed on the fluids of plants though a few species are predators of other insects.

Another distinct difference between true bugs and beetles can be seen in their wing structure. The beetle’s elytra (fore-wings) are entirely hardened and are not used for flight. These form a protective barrier for their alae (hind-wings). Both pairs of wings sit side by side and do not overlap, as they are in the true bugs. The true bugs also either have fully membranous wings or partially hardened elytra. In the case of true bugs with partially hardened elytra, the alae will be membranous, but many true bugs with membranous elytra will posses either reduced or completely lack their alae.

The final primary difference can be seen in their life cycle. Beetles are endopteryotes, meaning they go through a complete metamorphosis from a larval stage where as the true bugs are hemimetabolous and, after hatching, their young often appear as under-developed adults, known as nymphs. Often lacking wings until being gained during a molting (the most well known case of this, and also a member order Hemiptera, is the cicada) stink bug nymphs still possess the ability to produce the noxious chemicals found in the adults, though sometimes in a less developed way.

All members of superfamily Pentomoidea (which gets its name from these insects trade-mark 5 segmented antennae) either have a rounded or somewhat triangular body plan. Most in North America are more familiar with the angular body plan, but both forms are common. One of the easiest ways to tell if you are dealing with a member of this superfamily (other than the often nauseating odor when they are disturbed) is their well developed scutellum. This is a hardened extension of the thorax that covers the abdomen and protects part of the insect’s body and its wings, it is also the source of the common names ‘shield bug’ and ‘chest bug’. The scutellum is often mistaken as the hardened fore-wings of the beetles despite not being a part of the wing structures. Instead, the fore-wings are partially hardened and leathery to cover the membranous hind-wings, which are the primary source of flight. This combination of hardened and membranous wings gives the insect its characteristic buzzing sound while in flight.

Because of many stink bugs feeding off of the fluids of plants, many are considered major agricultural pests. A prime example of this can be seen with the introduction of the Brown Marmorated Stink Bug (Halyomorpha halys) to the North-Eastern United States from various parts of East Asia where it is also a common agricultural pest. First spotted in 1988, this species has quickly spread and now threatens crops as diverse as apples, sweet corn, peaches, soy beans, blackberries and others. Besides the damage to crops, many species of stink bugs are also common household pests where their repulsive sent makes many homeowners unsure of how to remove them without causing the insects to release their defensive chemicals. Despite being a common pest, some stink bugs are desirable due to their predatory nature, often feeding off of insects considered pests themselves.

The Brown Marmorated Stink Bug.

Many stink bugs take advantage of a survival technique known as clustering. This occurs when multiple insects congregate to increase their chances of survival as a group and, in some species, to mate. This form of aggregation is often aided by pheromones many species use to attract other individuals and mates. If these pheromones are present, they are typically produced by exocrine glands on the abdomen. It seems a wise maneuver to move in numbers when many animals are afraid to take on one insect, let alone risk a potential sudden cloud of terribly smelling chemicals.

But I’m sure what many of you have been waiting to read involves the source of their most common of names. This has to do with a defensive measure that most members of superfamily Pentatomoidea share to one degree or another, the use of chemical weaponry. Housed in special glands found on either side of the thorax, these insects emit of spray of odiferous chemicals. The nature of these chemicals varies from specie to specie with the most common derivatives being alcohols, aldehydes and esters. In a few species, the compound is based off of cyanide and has the poison’s trademark almond like scent, though despite being based on a potent toxin, exposure is not fatal to humans. It should be noted that there are a few insects that also posses foul smelling chemical defences that have no relation to the true stink bugs. These include the pinacate beetles (genus Eleodes) and the Box Elder Bug (Boisea trivittata) amongst others.

While few can tolerate the rancid smell if allowed to spray, some people have found another use for these pungent insects. As astonishing as it might sound for an insect notorious for its scent, many stink bugs are used in various cuisines from around the globe. Most commonly eaten in Vietnam, Laos and Mexico, they are often prized for their strong flavor.

Thank you Holte Ender for the request!

Adetomyrma venatrix, the Dracula Ant

For your average ant, work is grueling no matter what species you belong to. All working towards the common good and hoping the colonies lineage will be passed on, even if it takes the sacrifice of a few workers. But there is one species where sacrifice becomes a full time job.

To find it, you must search the Zombitse Forest. Yes, you are looking for ants in a forest in Western Madagascar that does not give you pause to consider the sanity of looking for something called Dracula Ants in amongst the brush which will be sure to be infested with tiny zombies. After the initial lamentations, you should be up to scowling out these tiny forest creatures.

Eventually you will find a colony of Adetomyma venatrix, the Dracula Ant. At first look you might be intrigued by the ants body form. Nearly a 'missing link', these ants resemble wasps more than ants. They have only one joint between their thorax and abdomen instead of three like other species of ants. They also have an elongated stinger as well as have lost the use of their eyes.

About now you are probably wondering why does this evolutionary curiosity have such a distinguished name as Dracula? Well this has to do with how they gain their nourishment. Normal ants have their larvae eat the food and pre-digest it for the workers and pass it along. But Dracula Ants are busy and need their nourishment a bit more...fluidic.

Hungary queens, drones, and workers need only chew open the head of one of their own young to find all the nutrients they could need. Their larvae have an abundance of blood, well actually, Hemolymph, which the adults of the colony can just drink their fill of.

When observed it is noted that the larvae are not fond of the arrangement in the least, as they try to crawl away when workers are present and tiny ant screams can even be detected as the adults drink their younger's vital fluids. The survivors then pupate into adult ants and continue the cycle of work and "nondestructive cannibalism".