Love gifts in the animal kingdom
On Valentine's day, what beau could possibly resist a hand-picked gift, wrapped in perfumed silk?
Certainly not female Paratrechalea ornata spiders, according to research by Dr Luiz Costa-Schmidt, an arachnid expert studying in Brazil.
Male spiders of this south-American species incorporate a chemical known as a pheromone into their silk gift wrap. This encourages females to accept them as mates.
Using a present, or "nuptial gift", to ensure a sexual engagement is a practice found throughout the animal kingdom but it can be startlingly different from our human perception of courtship.
Here are some of the weird array of presents that animals give to potential mates.Perfumed package
P. ornata are not the only spiders to give gifts to their intended: the male nursery web spider (Pisaura mirabilis), commonly found in European grass meadows, also wraps offerings in silk.
With this presentation, however, all is not as it seems. The males do not always wrap up enticing morsels of prey for their mates.
- Blue manakin birds troupe together to perform for a single female. The lead male then dismisses the troupe to close the deal
- Buff-breasted sandpipers flash their armpits to attract a female
- The superb bird of paradise performs a trance-like dance to attract the female
- Clark's grebes dance a watery waltz to reaffirm their affections
Instead, beguiling packaging can disguise a multitude of disappointing items - from dried-out ant husks to worthless bits of plant.
"If a male finds a receptive female, but [he] doesn't have prey at that moment, any object could be easily be wrapped in silk to be offered," explains Pedro Ere Disconzi Brum, another member of the Brazilian research team.
"This may be a crucial step for this male to be chosen by the female in the early steps of the courtship process."
Moreover, Mr Brum explains, if the male is in poor condition, he can catch prey for himself and wrap up the leftovers to gain the attention of a mate.
Dr Costa-Schmidt suggests that the key to this sneaky seduction could be scent.
"The male is probably exploring the female perception by adding a chemical signal that induces her to bite the gift," he explains.
When the female bites the gift she is momentarily distracted. So the male is able to take the opportunity to mate, regardless of the parcel's contents.Sickly sentiment
Male fruit flies meanwhile are much more direct: Drosophila subobscura simply regurgitate a nutritional liquid gift for potential mates.
Dr Michael Ritchie from the University of St Andrews, Scotland, has studied the exchange and tells BBC Nature that it is "harder to 'cheat' with vomit". For flies, the quality of the offering relates directly to the condition of the male.
Invertebrates have a fascinating (and often revolting) array of courtship gifts. Dr Karim Vahed from the University of Derby believes crickets are the most fascinating of all.
During mating, males present females with a "spermatophore" which Dr Vahed describes as "an edible, gelatinous substance which is attached to the sperm-packet".
The gift serves to feed and distract the female while sperm transfer takes place, but scientists have discovered many more layers of complexity to the exchange.
"While the gift is attractive to the female, it is not necessarily tailored to suit [her] nutritional needs," says Dr Vahed, citing tropical house crickets as an example.
He explains that, in this particular species, males offer low value gifts, but flavour them with feeding stimulants in order to trick females.
Dr Vahed has also found that the production of good gifts can be costly for males.
"It is known that producing a large gift delays males from re-mating, so males of species with large gifts would be expected to be more choosy," he said.
In a recent study of 54 different species, the biologist confirmed this theory. He found that the saddle-backed bush cricket (Uromenus rugosicollis) spent up to 104 minutes assessing a female before presenting its gift.
In contrast, the Polish species Leptophyes albovittata produced a spermatophore ten times smaller and mated after just 24 seconds.Fish dish
In the bird world, the male kingfisher is known as one of the most conscientious present pickers.
To woo a mate, males are required to swallow fish so that they can be presented to females with style: face first.
"Females are quite fussy - about both size and species," says wildlife filmmaker Charlie Hamilton James who has a particular soft spot for the birds.
"Males offering bullheads or stone loaches are less likely to succeed than males offering minnows - sticklebacks are somewhere in the middle.
"A fish that is too small is generally ignored."
Courtship does not always run smoothly for the brightly coloured birds. Mr Hamilton James notes that impatient males only wait around 10 minutes before giving up and eating the fish themselves.
"Sometimes the female will beg for fish and the male will ignore her and eat them in front of her," he adds.Meat for sex
Moving from fish to a meat course brings us to the sociable chimpanzee. And gift-giving behaviour among our closest cousins is currently the subject of much debate.
Professor Jill Pruetz, an anthropologist at Iowa State University, is currently studying savannah chimpanzees in Senegal.
Last year the team recorded males sharing wild plants and meat with non-related females. The exchange, though, did not necessarily result in immediate mating.
Likewise, in his study published in 2010, Dr Ian Gilby from Duke University, US, found the same lack of "response" by females to this male generosity in East African chimpanzees.
But research by Cristina Gomes and Christophe Boesch, suggests that male chimps could be playing "the long game".
Through close observation of a group in the Tai Forest reserve in Ivory Coast, they found that males sharing meat with a female over a long period of time increased their chance of mating with her.
"The Gomes and Boesch study is intriguing," says Dr Gilby, "In one way, their results are the same as ours - meat sharing did not increase the chances of an immediate mating."
"However, they found that a single sharing event increased a pair's probability of mating within the next several months."
Whether the females "remember" generous males or the meat-sharing creates a particularly strong bond remains to be resolved.
When it comes to animal tokens of affection, choice may be the female prerogative but males have more than a few tricks up their sleeves.