Archive for October, 2020

Spiders – you love them or you hate them. The latter is probably because you are afraid of them. It is hardly surprising, as the (inter)national media are full of spider-related nonsense with the only truth being that the news are about spiders which indeed exist: e.g., THE SCOTSMAN, Oct 1 2005: “Scotland is being invaded by new breeds of spider which are marching north as a result of climate change…” – DAILY MAIL, July 1 2005: “Gardener is left fighting for breath after a nip from the black widow’s distant cousin”. – THE WASHINGTON TIMES, Feb 27 2004: “A German man who kept more than 200 spiders in his home, along with other odd pets, was apparently killed and eaten by his critters”. No doubts, after reading this, anyone will get scared. Actually, the first two storylines are about False Black Widow Spiders (Steatoda species) representing part of the native British fauna and not dangerous. Reports on their bites are rarely/not backed up with formal spider identification.

Historically, spiders have become a traditional part of Halloween scare and even its symbol due to their suspected connection with witches. In medieval times, spiders, black cats and rats were believed to be evil companions of witches. Spiders are regularly depicted in horror films, occurring in and crawling out witch dwellings, vampire lairs or dungeons, and such places are always shown as being totally lined up with a thick layer of silk. Hence, no wonder people are afraid of spiders. But are spiders really that dangerous?

Pumpkin spider candle holder. © Jade Adrian

Spiders represent a very diverse group of organisms, with over 48,860 species being described worldwide to date. In Britain alone there are approximately 670 spider species, of which two thirds belong to the group known as ‘money spiders’ – tiny creatures with the body length less than 2 mm long. In the UK, there are NO spiders dangerous to man, rest assured about this. Nevertheless, how many of us could admire spiders or simply tolerate their presence: say, daddy-long-legs in own cellar or a house-spider in a bathroom?

Most/all common fears of spiders are because these awesome creatures are badly misunderstood. If one imagines a spider, two main features thereof immediately come to mind: venom and silk. Let us consider both features and some misconceptions connected to them.

1. All spiders are poisonous.

This is what people say and this is one of the main reasons why spiders are feared. Well, all spiders are carnivorous. They possess sharp fangs and kill their prey with a venomous bite. Thus, all spiders, except for one family Uloboridae, are venomous. But the common concern and fear are really about whether spiders are dangerous to humans?

Our ancestors seemed to be confident about this, depicting spiders as demonic, insect ghouls, with venom mouths. Sir Thomas Wyatt (1503–42) in his epigram ‘How by a Kiss he found both his Life and Death’ made known spiders as anti-bees gathering poison from a flower:

“Nature, that gave the bee so feat a grace

To find honey of so wondrous fashion,

Hath taught the spider out of the same place

To fetch poison, by strange alteration.”

In the 17th century, spiders and their bites were sometimes regarded as dangerous as nitric acid or rat poison. Even nowadays, there are lots of urban legends about “deadly” spiders, for instance, “The Daddy-longlegs Spider has the world’s most powerful venom”; “People can lose arms and legs because of spider bites”; “Deadly poisonous spiders lurk beneath toilet seats in airports”; “The spider found in the bath crawled out the plughole”; etc. Alas, none of these statements is true.

Male of House Spider (Eratigena duellica) did not crawl out the plughole, as some might think, it entered the house via the door searching for a possible mate. Just let it go. © H. Bellmann

In a simplified way, there are two different kinds of venom produced by spiders: neurotoxic and necrotic. Neurotoxic venoms work directly on the nervous system. The best known example is the venom of Black Widow spiders (Latrodectus species). Necrotic venoms cause damage to the tissues, such as ulcers and lesions. The best example is the venom of Recluse Spiders (Loxosceles species). More about spider bites here and here. However, we need to remember that although a dozen or so spiders (out of about 50,000 species known worldwide) are known to produce venom that is toxic to humans, none of these species occurs in the UK. Thus, in this country, there is no reason to fear spiders and their bites at all.

Cross section of spider carapace to show the position of poison glands. Modified from Foelix (2011).

2. All spiders make webs.

In our imaginary world spiders are capable of weaving silk in such large quantities that even a human body could be wrapped up, as it happened to poor Frodo Baggins in Shelob’s lair from ‘The Lord of the Rings’. Nothing could be more untrue than such nonsense (not to mention that the giant spider Shelob was depicted as a non-existing type of animal (even with a sting).

The English word ‘spider’ comes from the old English ‘spinnan’ via the Middle English ‘spither’ meaning ‘spinner’, and as such spiders frequently appear in English literature. For instance, Shakespeare used a spider in his ‘The Merchant of Venice’, Act III, Scene II:  “Here in her hairs / the painter plays the spider, and hath woven / a golden mesh t’entrap the hearts of men”. Yes, all spiders can produce and weave silk. However, although all spider webs are made of silk – the material of outstanding mechanical properties (or here) – not all spiders build webs for prey capture. Many actively hunt for their prey, as reflected in their names: jumping spiders, lynx spiders, wolf spiders, etc. Yet all spiders use silk for producing egg sacs, retreats, moulting or mating chambers, draglines, and some of them for making catching devices. Many spiders use silk threads for ballooning and this way can disperse for long distances, sometimes for hundreds of miles (watch the video below). This is why in the Medieval English bestiaries, spiders were described as aerial worms that take their nourishment from the air.

I you are walking in the countryside and accidentally have a silk thread across your face, there is nothing to worry about – it is likely to be gossamer, and hence the time for St Martin’s summer, Martinmas in a church and a goose to be cooked and eaten… By all means silk production by spiders has no effect on our life, apart from the need to clean dark corners of our houses, and in this respect there is no need to worry or fear spiders at all.

Male of common European jumping spider Aelurillus v-insignitus is looking at you. Is not it cute? Are you really still scared? © Barbara Thaler-Knoflach

Further reading:

Foelix R.F. 2011. Biology of spiders (third edition). Oxford Univ. Press., 420 pp.

Hillyard P. 1994. The book of the spider. New York: Avon Books, 218 pp.

Marren P. & Mabey R. 2010. Bugs Brittanica. London: Chatto & Windus, 500 pp.

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Male of Euglossa heterosticta approaching flowers (right) and landed on them (left), La Selva Field Station, Costa Rica, June 2018; © M. O’Donnel.

Honeybee males are called drones (see also here). They do not have sting, do not make honey, do not even feed themselves but are rather fed by worker bees; their primary role is to mate with virgin queens. As result, drones have acquired a rather negative reputation among humans. From the ancient times till now, drones have been regularly described as ‘lazy loudmouths’, ‘greedy lozells’ or even ‘virulent weeds, to be eradicated’ (Fig. 1). They “lazily consume the labours of the bee” – said Hesiod in his Works and Days (c. 700BS); so drones were not even seen as the bees. Thomas Moffet (1658) in his Insectorum wrote about drones:

Both God and man disdain that man

Which Drone like in the blue,

Nor good nor ill, endeavour can

Upon himself to live,

But idle is, and without sting,

And grieves the labouring Bee,

Devouring that which he home brings,

Not yielding help or fee.”

Fig. 1. Greedy drones, as depicted in Cotton’s Buzz-a-Buzz. © The Bodleian Libraries, The University of Oxford. In the frame at the left top corner, a honeybee drone from the collection of the Manchester Museum.

Sometimes drones are depicted as indolent, small-brained creatures that are anatomically unfitted for foraging, in other words, for doing THE important job – i.e., collecting nectar and making honey for us, humans. Indeed, what impudence!

Perhaps drones are not altogether idle and do help in warming and cleaning the hive, and secreting a special jelly used for feeding brood. Yet the truth is that after the breeding season all drones are evicted from the hive or slaughtered by female workers if they resist eviction. Their life is short and basically serves one purpose only – mating, but who would dare to say that this JOB is not important?

However, drones in some other groups of bees, for instance, orchid bees (see also here) demonstrate a far more complex lifestyle and are notable for their important role in pollination, especially of orchids – this is why their name. As the famous Spanish poet Antonio Machada (1875–1939) put it, “Bees, singers not for the honey but for the flowers”. Orchid bees are also distinguished by their shiny metallic coloration and resemble living jewels (Fig. 2).

Fig. 2. The male orchid bee Exaerete smaragdina from Costa Rica in the insect collection of the Manchester Museum. © The Manchester Museum.

Orchids are the most species rich plant family, accounting for more than 10% of all flowering plant species. Male orchid bees pollinate over 25% of the orchid species (c. 2,000) from tropical Americas. More than 600 orchid species depend solely on male orchid bees for pollination. Males do not specialize in one or a few orchids and visit many different species. Although females of some orchid bees pollinate nectar-producing orchids such as Sobralia (in that mode resembling other bee pollinators), it’s the males that are much more important in orchid pollination. This unique mode of pollination is sometimes called the ‘perfume flower syndrome‘ – that is a selective attraction of male orchid bees to orchid flowers.

Male orchid bees are strong flyers. While visiting numerous flowers, individual males are able to travel long distances from 400-800 m to 5-6 km in a single trip, or even to cross the distance of 45-50 km within a few days. The longest flight distance ever recorded for a male orchid bee (Euglossa viridissima) from Yucatán, Mexico was 95 km, crossed in 12 days. Isn’t that an impressive achievement for a housefly-sized creature?

But why do male orchid bees visit orchids and other flowers? Certain flowers are visited to feed on nectar and pollen, as all bees do. However, males do not collect nectar for producing honey. Making honey is still the duty of orchid bee females. Yet the majority of flowers visited by drones usually lack nectar but are very fragrant, with bees being attracted by flower scent. Indeed, they visit flowers to collect aromatic compounds to render themselves attractive to females, and also for chemical signalling to their rivals during territorial display. Males also collect fragrances from non-floral sources, such as plant wounds, fungi or even rotten wood.

Fig. 3. Male of Eulaema cingulata from the collection of the Manchester Museum: A – brusher of the front tarsi; B – tibial organ of the hind legs, modified from Dressler (1968: fig. 1).

While visiting a flower, a male brushes on the surface of the flower with hair pads of its forelegs (Fig. 3), collecting the fragrance oils. Usually the bee brushes for a short time, then hovers near the flower and transfers the collected substance via midlegs to a specialized hollow pocket in its enlarged hind legs in which the scents are stored. The male repeats this behaviour many times, sometimes remaining on one flower or inflorescence as long as 90 minutes. This behaviour is shown on the following short video.

Drone receives a pollen sac (=pollinarium) as it leaves the flower or during collecting fragrance oils, as shown in Fig. 4. Pollinaria are usually glued to a dorsal side of bees: head, thorax or abdomen (Fig. 5), also to antennae and legs. Individual bees often can carry the pollinaria of more than one orchid species. Having received pollinaria, drone flies away and then visits another flower of the same orchid species where the pollinaria are detached and pollination takes place.

Fig. 4. Pollination of the orchid Stanhopea grandiflora by male orchid bee Eulaema meriana: (A) The bees enters in the saccate base of the flower lip; (B) The lip is very smooth and slippery, the bee may fall while withdrawing, attaching pollinaria (in yellow) to its thorax; (C) Dorsal view of the bee with the pollinaria attached; (D) Outline of the bee showing placement of the pollinaria from side. Modified from Dressler (1968: fig. 2).

Many orchids are very scarce in nature, with individual plants being separated from each other by long distances. Therefore, male orchid bees are to be really strong flyers to visit several flowers of such orchids in a single trip. Indeed, these bees are strong flyers (see above).

Fig. 5. Outline of an orchid bee male showing how pollinaria of different orchid groups can be attached: (A) Notylia; (B) Lacaena; (C) Mormodes, goblin orchids; (D) Cycnoches; modified from Dressler (1968: fig. 4). On the right: male of Euglossa imperialis from Costa Rica carrying two pollinaria, © J.H. Marden.

According to one hypothesis, the main reason why male orchid bees collect floral fragrances is that it helps them to be more competitive when mating. A female seems to choose a potential mate based on its ‘quality’ which is associated with the complexity of a perfume presented by the male. Females prefer males with more complex bouquets, which can contain up to a dozen of aromatic compounds. A complex perfume is correlated with greater male fitness: i.e., its strength and physical characteristics. The male that is able to fly long distances and to visit more flowers can present a more complex bouquet; it also means that such male lived longer and hence its survival rate is higher. As male physical characteristics are heritable, the offspring from a stronger male will have higher chances to survive.

The orchid bees’ attraction to floral scents is used to study their diversity, daily activity, flight ranges, etc. by means of chemical baits. Please, watch the following video on how to attract and count orchid bees.

Further reading

Birchall E. 2014. In praise of bees. A cabinet of curiosities. Quiller, Shrewsbury, UK, 256 pp.

Cameron S.A. 2004. Phylogeny and biology of Neotropical orchid bees (Euglossini). Ann. Rev. Entomology, 49: 377-404.

Dressler R.L. 1968. Pollination by Euglossine bees. Evolution, 22(1): 202-210.

McHatton R. 2011. Orchid pollination: exploring a fascinating world. Orchids, June: 340-349; online

Roubik D.W. & Hanson P.E. 2004. Orchid bees of tropical America. Biology and field guide. Sna Jose: INBio, 370 pp.

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