Silba adipata McAlpine

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Home > Living Habits > Detecting the Black Fig Fly.

 

Author: François DROUET.
Photographs / videos: F. DROUET
(unless indicated).
All rights reserved.

 

 

Detecting the Black Fig Fly

 

 

 

According to the following plan: the flight pattern (a major detection mean), where to find the Black Fig Fly on the fig tree? Activity periods during the day, Black Fig Fly accessibility.

 

THE FLIGHT PATTERN: A MAJOR DETECTION MEAN

 

FLIGHT PATTERN

The Black Fig Fly walks slowly, but its flight is very fast. And it has a characteristic which enables to easily identify the species (with some practice…): it is a sharp zigzag flight, composed of permanent back and forth 30-50 cm in length, in all directions. When very close to the targeted leaf, twig, or ripe fig, the Black Fig Fly moves back and forth much shorter (about 5 cm ), and progressively slower, before ending up landing.

 

Silba adipata McAlpine Flight pattern.

 

This flight pattern is a major detection mean, because (especially if several flies are involved) it induces a lot of movements at the fig tree periphery that we cannot miss.

Inside the fig tree, the Black Fig Fly moves from one place to another by shorts direct flights, but keeping its specific lively zigzag flight pattern, even for a very small distance. It can thus be quite easily recognized.

The videos provided in the chapter dedicated to the Black Fig Fly flight will help for identifying it via its flight pattern.

Note: it is not uncommon to find zigzagging insects around the fig tree, or flying through the fig tree. Special attention should be paid to two points to avoid confusion with the Black Fig Fly's flight pattern: generally, these insects have a much slower zigzagging flight ; and, they fly more or less horizontally, not coupling to their zigzags a sharp repetitive vertical displacement (as the Black Fig Fly does).

 

CAN WE HEAR THE BLACK FIG FLY WHEN IT IS FLYING, AND THUS DETECT IT?

The flight of the Black Fig Fly is perfectly silent, whatever the distance at which the insect is, and whatever the circumstances (approach flight towards the fig tree, moving from one point to another in the fig tree to feed or to lay eggs, sudden take-off following a movement that disturbs it...). And this, even if the black fig flies are two or three to fly together.

I can no longer count the number of times a black fig fly suddenly flew away when I had approached the camera to 1 cm from it, so when it was to 20 cm from my ear, and I never heard it despite the surprising speed of its flight.

Over the years of observing the Black Fig Fly, I have had the opportunity to experiment close contacts with it, and all of which confirmed the absence of sound detection possibility of its flight. For example, when black fig flies came and landed on my camera while I was photographying them, or more rarely when a black fig fly landed on my trousers at the observation post in the field, or at home when I practiced black fig flies breeding.

Note: the Black Fig Fly's flight cannot be detected by sound, but this character constitutes a discriminating factor: any look-alike fly which would be detectable by sound during its flight can be considered without a doubt as not being the species Silba adipata McAlpine.
 

Black Fig Fly (Silba adipata McAlpine) : flight.

A black fig fly joining two others to feed on a cut fig tree leaf petiole.

 

WHERE TO FIND THE BLACK FIG FLY ON A FIG TREE?

 

It is difficultt to see the Black Fig Fly on a fig tree.

The fisrt reason is its tiny size (most often 4 mm long).

The second reason is that, during its stay on the fig tree, it remains almost all of its time on the underside of the leaves, on which it directly lands, and where it feeds and performs its perpetual grooming activities, walking slowly or keeping motionless during long whiles. It rarely lands or walks on the upperside of the leaves, that it does not appreciate. Most often, a black fly on the upperside of a leaf is not the Black Fig Fly, but one of its lookalikes.

To increase the chances for seeing the Black Fig Fly, it is advisable to especially examine the shaded or semi-shaded parts of the fig tree, because it does not like the sun (even if it is protected from it by the leaf under which it remains). And to look under the leaves of the periphery, because the Black Fig Fly does not directly lands under those of the inside.

The Black Fig Fly is never on the trunk or on the gray wood (branches, twigs one year old and more), which do not attract it. It lands and walks only on the twigs of the year, which are green, then turn brown during the season.

Regarding the figs, the Black Fig Fly is not interested in the unripe green figs for feeding and it is rarely found on one of them. But it is greedy for ripe and overripe figs, on which it most often directly lands.

The case of an egg-laying Black Fig Fly female which arrives on the fig tree is quite particular: from its arrival until its departure after having performed its sequence of successive ovipositions (up to 20 visited unripe figs), it touches only green unripe figs and cannot be seen on any other part of the fig tree.
 

Black Fig Fly (Silba adipata McAlpine) on the underside of a fig tree leaf.

A black fig fly on the underside of a fig tree leaf.

 

Black Fig Fly (Silba adipata McAlpine) on the underside of a fig tree leaf.

A black fig fly on the underside of a fig tree leaf.

 

ACTIVITY PERIODS DURING THE DAY

 

Regarding the Black Fig Fly activity periods during the day, I have observed two very different behaviors, depending on the type of activity: feeding or egg-laying.
 

FEEDING ACTIVITY

Feeding constitutes the main part of the Black Fig Fly activity on the fig tree, and I observe a strong activity for two periods in the day.

The first is the early morning. The feeding activity begins when the sun rises. More precisely, when it is not yet directly striking on the foliage, but the day is already clear. Then the feeding activity continues until the sun strongly strikes on the whole fig tree. The second is the end of the afternoon and twilight, and even more when nightfall is approaching. It may happens that I observe a very reduced activity later in the morning or earlier in the afternoon, but it is rare.

Within the two feeding activity periods, I have remarked the existence of usual attendance times: for one given fig tree, the feeding black fig flies are present in the same time slots from one day to the next. This whatever the month in the season, and for fig trees of various varieties. For example, in June 2016, they daily arrived from 4 pm to 4.30 pm on my ‘Bellone’ fig tree, and in September of the same year, they daily appeared from 6 pm to 6.30 pm on my ‘Col de Dame Noire’ fig tree.

I add that, for one considered fig tree, as it exists usual attendance times, it exists usual attendance areas: during the day, the black fig flies frequent a preferred area on the fig tree, the same from one day to the next (and the same from one year to the next…).

So, if you detect feeding black fig flies on a fig tree, note the time and the concerned area on the tree. The following days, come and observe the black fig flies at the same time and in the same fig tree area. Of course, this a general phenomenon, which may suffer from some exceptions. Moreover, I think that everyone should check in his own orchard the existence of usual attendance times and usual attendance fig tree areas, for which  I only have observations carried out in my orchard.
 

Black Fig Fly (Silba adipata McAlpine) feeding on a fig tree (latex ooze).

Three black fig flies feeding on the fig tree (latex ooze).

 

EGG-LAYING ACTIVITY

For the egg-laying activity, my observations relative to the activity periods during the day are different (for details, see the chapter "Intense attacks phase characteristics").

For one given fig tree, during the intense Black Fig Fly attacks phase in the season (concentrating 75 to 97 % of the attacks during 12 to 23 days), I have observed that the ovipositions have no particular occurrence periods during the day. They are randomly distributed in all the time slots of the day.

But I have noted that for one considered fig tree, the egg-laying activity is discontinuous during the day (up to several hours without any egg-laying females on the tree), altough it is regular thoughout the week (egg-laying females can be observed each of the days on the considered fig tree).
 

Silba adipata McAlpine: egg-laying activity.

Silba adipata McAlpine: egg-laying activity.

 

BLACK FIG FLY ACCESSIBILITY

 

Concerning the contacts that I had the opportunity to live with the Black Fig Fly, I can report an extremely rare direct physical contact.

In September 2016, I was photographying a black fig fly feeding on a ripe fig of the 'Col de Dame Noire' variety, when I saw in lateral vision at 50 cm from me the characteristic flight of an individual of the species. I stepped back slowly, hoping to be able to photograph it together with the other. Holding my camera only in my right hand, I was surprised to see that the black fig fly landed, not on the ripe fig as I hoped, but on the top of my left hand, which was horizontally at 20 cm from the camera.

It began to walk slowly over the top of my hand, licking it with its unfolded oral tube. When it approached the edge of the hand, I turned the latter very slowly so that the fly passed over the palm while continuing to walk. The black fig fly even climbed along my fingers, and it stayed thirty to forty seconds on my hand, before vigorously but silently flying away.

I think that the black fig fly was attracted by the presence of latex traces on my hand. A few moments before, I had handled the petioles of fig tree leaves torn off to cause latex oozes. Below, my exceptional encounter with the Black Fig Fly. 
 

An exceptional encounter with the Black Fig Fly (Silba adipata McAlpine, 1856).

My exceptional encounter with the Black Fig Fly.

 

An exceptional encounter with the Black Fig Fly (Silba adipata McAlpine, 1856).

My exceptional encounter with the Black Fig Fly.
 

During my photography sessions of black fig flies at home (flies from my breeding), I saw only once one of them land on me.

Among other exercises, I photographed them in close-up on my kitchen window glass. I used to gently drop down with a long and very thin wand those that had climbed too high while walking, so that they landed lower on the glass after quickly freeing themselves from the wand tip by a short vertical agitated flight (when they did not fly off to stick to the ceiling ...).

One of the flies dislodged from the window glass landed on my leg, as I sat down to rest while continuing to photograph. I did not move my leg and it stayed for about thirty seconds before spontaneously leaving it, perhaps not finding to her liking the canvas of the jeans I was wearing ...
 

A black fig fly on the observer's jeans.

A black fig fly companion on my jeans.

 

A black fig fly on the observer's jeans.

A black fig fly companion on my jeans.
 

In the field, during my many hours of observation and photography, I only experienced the same situation on two occasions: a black fig fly landed on the top of my leg, while I was sitting at the observtion post. But the fly did not stay very long, and I was not able to benefit from a good light incidence to achieve fairly sharp photographs.

 

 

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