Insect overview

Insects are invertebrates; they sport an external skeleton rather than internal bones.  Their limbs are jointed, they’re cold-blooded, have six legs and (mostly) two pairs of wings.  Their body is split into three sections; the head, thorax and abdomen.

Any insect can be split into three parts.  There’s a head (box-shaped and containing the insect’s sense organs and mouth).  The there’s a thorax (the middle, where the wings and legs attach).  Finally,  there’s an abdomen (the rear section where breathing and digestion/ excretion/ reproduction occur).

The Head

Insects sense the world around them with eyes.  These can be simple or made of many lenses (compound).  Some insect eyes merely detect light and dark; others can see all the colours we see, plus ultraviolet light.  A top insect predator, such as a dragonfly, has thousands of lenses building up its compound eye and their eyesight is pretty acute.  (For more on dragonflies, check out my blog.)

Antennae are attached to an insects head and let it smell, taste, and touch the world around it.  They pick up vibrations too.  Like most insect features they vary wildly from animal to animal.   Consider the incredibly long antennae of a blind cave cricket next to the furry ones of a moth.  The first sort senses the area around the insect, the second picks up pheromones and helps locate a mate.

Insect’s mouths allow the insect to feed.  However, some insects don’t eat as adults (the mayfly for example), and have no mouths at all.  With food stuff as varied as leaf-litter to other insects, seeds to wood and meat, insect mouths have evolved into a regular toolbox for feeding.  Crushing, slicing, sucking through straws, chewing through trees – insects have evolved them all.  Mouths also can also get rid of waste products, deliver bites, and produce silk and venom.

The Thorax

This is the power-house of the insect.  Wings and legs are attached to this box-like structure; within it lie the muscles to drive locomotion.

Legs are segmented and are are used for walking, jumping, swimming, and digging.

This Harlequin beetle, Acrocinus longimanus, has extraordinary legs which it uses to attract females, and to get across tree branches in its South American rainforest home.

Feet are good for gripping and cleaning; they may have sensitive hairs which help the insect feel danger from behind.

Insects have two pairs of wings; forewings (at the front) and hindwings (behind).  These are used for flight and display.  Some insects have lost their wings entirely (like the ants) whilst others have adapted them enormously.  Beetles have evolved their forewings into tough coverings, or elytra, which enable them to exploit all sorts of habitats.  This doesn’t compromise their ability to fly.  Flies  have adapted their hindwings into tiny lolly-pop like structures called halteres.  Halteres work like gyroscopes, allowing complete control over rotation and direction when flying.

The blue-bottle fly, Calliphora vomitoria, showing halteres.  These are easiest to see on a crane fly (daddy long-legs).

The Abdomen

Insect abdomens are the site of digestion, excretion, circulation, and respiration.  Their hearts are here, and although different to ours they do the same job.  They pump blood around the insect’s body.  Insects breathe through their abdomens too, through small holes called spiracles which connect to internal tubes (trachea). These  connect to smaller tubes (tracheoles) which terminate in water filled spaces of 1 micrometer or less. This is where gas exchange occurs.

Caterpillars are good subjects if you want to see spiracles; they often appear as dark spots along the animal’s side.  This one’s a tobacco hornworm (Manduca sexta).

The most wonderful thing about insects is their adaptability, they’ve taken this basic body plan and run with it in thousands of different evolutionary directions.  To see if you’ve got the basics sorted, try to identify all the key insect features on the insect illustrations below.

There’s so much to say about insects, and how magnificent they are, that it’ll doubtless be a topic I return to.  For more on insects, and for links to help learn more, have a look at the Amateur entomologists society page.

The post Natural History Illustration: Insect anatomy appeared first on Lizzie Harper.

Sources of information on Fruit type

This got me thinking about how little I knew about  fruit types.  I thought if I blogged on the subject I’d learn a bit more.

I’m using the glossary from Flora of the British Isles by Clapham, Tutin, and Moore for my definitions (which I’ll quote, or paraphrase); it’s an eminently accessible and well-loved tome.  I used it throughout my work on the plates of the Collins Flower Guide by David Streeter.  It’s reccommended by both the Botanical Society of the British Isles (BSBI) and numerous botany departments of British colleges.

Defining terms used to describe fruit

Before we start on the fruit types, we need to define a couple of terms.  A CARPEL is an organ at the centre of a flower, which carries one or more OVULES (“an ovule is a structure containing the egg, and which develops into a seed after fertilization”), and whose margins fuse with other adjoining carpels to make a safe space where the ovules and ovary (and subsequently the seeds) are enclosed.  A GYNOECIUM is the female part of a flower (so the ovaries and, once fertilized, the seeds) along with the style and pistil.  A LOCULE is a segment, or chamber within the fruit.

Capsule

First up, the CAPSULE: “A dry dehiscent fruit composed of more than one carpel”.  If a fruit is dehiscent, it means it breaks open at maturity, in this case to spread the seeds.  The number of locules borne by a capsule varies from species to species, and mono/ bi/ tri-locular are just terms used to refer to these differences.  Examples of capsule-bearing plants are many lilies, the brazil nut, the horse chestnut, and the poppy family.

Berry

BERRY is a commonly used term, and (amazingly and luckily) mostly used in a botanically correct way. It’s a “fleshy fruit, usually several-seeded, without a stony layer surrounding the seeds.”  They’re produced from a single ovary. Lots of the fruit we eat are berries.  Blue-berries, gooseberries, grapes, tomato, elderberry come to mind.  Edible fruits we wouldn’t think of as berries are, (botanically), also berries.  These include pumpkin, watermelon, avocado, and coffee.

Legume

LEGUMES are dry fruit that develop from a lone or simple carpel.  They dehisce (break open) along two seams (one on each side) when ripe.  They are referred to as “pods”.  Think of the bean and the pea.  Any member of the Leguminosae (now called Fabaceae) have legumes.  Alfalfa, clover, letils, beans, lupins, peas, and vetch are examples.  Black locust (below) is one of the only legume-bearing trees.

Pome

POME are fruit “in which the seed is surrounded by a tough but not woody or stony layer, derived from the inner part of the fruit wall, and the whole fused with the deeply cup-shaped receptacle.” So pomes have seeds deep within thick layers (which, in the case of apples and pears, we eat).  You can see that it fuses with the receptacle because when you eat an apple, the stalk goes direct into the fruit. The “core” of an apple are the carpels, all fused together. Examples of pomes are apples, quince, pears, hornbeam, and hawthorn.

Cypsela

CYPSELA.  Ah, now here we get into some trouble.   Several fruit types explained here are actually different sorts of ACHENE.  An achene is a “small, dry indehiscent single-seeded fruit”.  In fact there’s such diversity in this definition that I’m going to do a whole blog on achenes.  For now though, a cypsela is an achene which develops from a compound inferior ovary.  They’re fruit of the Asteraceae family, so plants like dandelion and sunflowers.  If you think of a dandelion seed, the “wing” or parachute of it is actually an extension of the calyx (all the sepals), the seed and surround is the cypsela.

Achenes

ACHENE.  “a small, dry indehiscent single-seeded fruit”.  As I say, there’s tons of diversity wtihin this definition, mainly based on the position of the seed in the achene or the structures surrounding it.  Suffice to say that plants as diverse as the dandelion, elm, strawberry, rose, sycamore, and buttercup bear achenes.  As I mentioned earlier, next week’s blog’ll be all about achenes, so keep an eye out for it.

Drupe

Next up is the DRUPE, a “fleshy fruit with one or more seeds, each surrounded by a stony layer”.  Pretty straight-forward.  Drupes include damsons, plums, sloe, and ivy.

Caryopsis or grain

I’m afraid the CARYOPSIS is another form of achene.  It’s an achene where the ovary wall and seed-coat are united.  In effect, this means it’s a seed that’s only got one (fused) layer covering it.  This is the way that all the grasses and cereal crops bear their fruit, and the simplest way to think of it is as a lone grain of sweetcorn (maize); in fact “grain” is aonther word for a caryopsis.

Schizocarp

A SCHIZOCARP is an ovary formed of lots of fused carpels (SYNCARPOUS) that splits into separate segments when ripe; each segment has one seed.  It can also be defined as any fruit which splits into different portions when mature.  Examples of schizocarpous plants include carrots, mallow, and parsley.

Samara

I rather like the SAMARA, winged achenes; or “dry indehiscent fruit part of the wall of which forms a flattened wing”.  Trees often bear samara, and the wing is brilliant at using the wind to disperse.  Just watch a maple samara twist to the ground, or some ash keys helicoptering down.  Very clever.  Elms, the hop tree, ash, and maples all produce samaras.

Siliques

SILIQUES are specialised capsules which dehisce from below, with the ovary walls (the VALVE) lifting away to reveal the seeds supported by an internal scaffold (the REPLUM).  They’re formed of two fused carpels, and their length has to be more than 3x their width.  Examples include radish, bittercress, and oil-seed rape.

Nuts

Wa all know what a NUT is, and eat lots of different types.  They tends to be single seeds encased in a hard outer ovary wall which doesn’t dehisce or easily part from the wall (or “shell”) at maturity.  The ovary wall tends to be woody, and true nuts develop from compound ovaries.  Species bearing nuts include hazel, chestnut, beech, and oak.

Follicle

Finally, the FOLLICLE is a “dry dehiscent fruit formed of one carpel, dehiscing along one side”.  It has two or more seeds which get dispersed when the follicle splits along one seam at maturity.  Examples include the peopny, milkweed, hellbore, larkspur, and aquilegia.

And that’s it!  Most of the different terms for a fruit defined.  I feel it’s one of these areas where if I use the terminology more then I’ll get used to it, and no longer feel over-whelmed by so many terms and definitions.  And certainly, for me, matching a plant to its’ fruit type has been highly instuctive.  I just hope I’ve not bored you to tears as I did it!

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