Saturday
Aug312019

Seasonal variation in the numbers of Delia Platura

Another bivoltine species, at least in southern UK.  Again based on specimens collected between 2014 and 2019, mostly in the Reading area but with a few from north Yorkshire and a few from the New Forest.

Monday
Aug262019

Bramble Stem Gall

A stem gall on bramble (Rubi fruticosus) caused by the larvae of the wasp Diastrophus rubi (Hymenoptera: Cynipidae). Identified using the key of Redfern & Shirley, 2011.

For images of the contents and later stages of these galls see here.

Specimen take in Thames Valley Park, Reading, UK on 2019-08-26.

Monday
Aug192019

Spring and Autumn Flies

More seasonal frequency plots for Muscid flies: First Eudasyphora cyanella which is commonest in spring:

And, second, the closely related Eudasyphora cyanicolor which is commonest in autumn:

These are from flies caught between 2014 and 2019 mainly on the Reading area but with with some from North Yorkshire and the New Forest.

Saturday
Aug172019

Seasonal variation in the numbers of Phaonia subventa

I have written a little script to help me create plots showing the seasonal variation in the numbers of various species of fly I have collected.

Most species show a large peak in numbers in late spring or early summer with none or very few in winter.  The Muscid fly Phaonia subventa is unusual in showing fewer flies in the summer than in the winter.  I had noticed that it was one of the most common woodland flies in winter (I have seen them on Christmas day morning, sunning themselves on tree trunks when the temperature was below 5C) but I hadn't realised, until I saw the above plot, that they seem to almost completely disappear during the summer months. This might be that this is is a consequence of the dry summers we have had in the south of England in the past few years.

My script is still a bit primitive (it is written in Gnu Awk!) and I intend to tidy it up and extend it (and maybe rewrite it in Rust).  But if you are interested you can find a copy in the Github repository where I store the catalog of my fly collection (https://github.com/tristrambrelstaff/flies).  The script is mplot.gawk.

Thursday
Jul112019

How to make a PDF document searchable

I had a large PDF file that I wanted to be able to search quickly but it just contained images of text, not the actual text itself, so all searches in it failed.

I use Ubuntu so I reasoned that there should some solution for me available out on the Web.  There was.  This is the one I chose:

Install pdfsandwich:

sudo apt-get install pdfsandwich

Run pdfsandwich on the file you want to become searchable:

pdfsandwich test.pdf -o test-searchable.pdf -nthreads 12 -first_page 5 -last_page 290

Here I use the -nthreads option to prevent pdfsandwich from locking up my computer by using all of its 16 processors.  I also use the -first_page and -last_page options to exclude the table of contents and the index from the searchable area (these just produce unnecessary duplicate search results).  The -o option specifies the name of the output file.

The resulting file was less than a tenth the size of the original (20MB instead of 350MB) so the text and images were more grainy but they were still easily readable. And being able to search it quickly makes the document much more useful to me than the original was.